Metal powder for powder metallurgy, compound, granulated powder, and sintered body

ABSTRACT

A metal powder comprising particles, which contain Fe, Cr, Si and C, and in which when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a higher group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a higher period number in the periodic table than that of the first element is defined as a second element, the first element is contained in a proportion of 0.01% by mass or more and 0.5% by mass or less, and the second element is contained in a proportion of 0.01% by mass or more and 0.5% by mass or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2015-023385 filed on Feb. 9, 2015. The entire disclosures of Japanese Patent Application No. 2015-023385 is hereby incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a metal powder for powder metallurgy, a compound, a granulated powder, and a sintered body.

2. Related Art

In a powder metallurgy method, a composition containing a metal powder and a binder is molded into a desired shape to obtain a molded body, and the obtained molded body is degreased and sintered, whereby a sintered body is produced. In such a process for producing a sintered body, an atomic diffusion phenomenon occurs among particles of the metal powder, whereby the molded body is gradually densified, resulting in sintering.

For example, JP-A-2012-87416 proposes a metal powder for powder metallurgy which contains Zr and Si, with the remainder including at least one element selected from the group consisting of Fe, Co, and Ni, and inevitable elements. According to such a metal powder for powder metallurgy, the sinterability is enhanced by the action of Zr, and a sintered body having a high density can be easily produced.

The thus obtained sintered body has recently become widely used for a variety of machine parts, structural parts, and the like.

However, depending on the use of a sintered body, further densification is needed in some cases. In such a case, a sintered body is further subjected to an additional treatment such as a hot isostatic pressing treatment (HIP treatment) to increase the density, however, the workload is significantly increased, and also an increase in the cost is inevitable.

Therefore, an expectation for realization of a metal powder capable of producing a sintered body having a high density without performing an additional treatment or the like has increased.

SUMMARY

An advantage of some aspects of the invention is to provide a metal powder for powder metallurgy, a compound, and a granulated powder, each of which is capable of producing a sintered body having a high density, and a sintered body having a high density.

The advantage can be achieved by aspects of the invention described below.

A metal powder for powder metallurgy according to an aspect of the invention includes particles, which contain Fe as a principal component, Cr in a proportion of 0.2% by mass or more and 35% by mass or less, Si in a proportion of 0.2% by mass or more and 3% by mass or less, and C in a proportion of 0.005% by mass or more and 2% by mass or less, and in which when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a higher group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a higher period number in the periodic table than that of the first element is defined as a second element, the first element is contained in a proportion of 0.01% by mass or more and 0.5% by mass or less and the second element is contained in a proportion of 0.01% by mass or more and 0.5% by mass or less, wherein the content of Cr on the surface of each particle is 0.2 at % or more and 15 at % or less and is 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle.

According to this, the particles of the metal powder for powder metallurgy each have a passivation film derived from a Cr oxide whose thickness is small to some extent, and therefore, the decrease in the sinterability of the particles due to the passivation film can be suppressed. As a result, the densification during sintering of the particles is achieved, and thus, a sintered body having a high density can be produced without performing an additional treatment.

In the metal powder for powder metallurgy according to the aspect of the invention, it is preferred that the content of Si on the surface of each particle is 155% or more and 800% or less the content of Si at a depth of 60 nm from the surface of the particle.

According to this, Si is segregated on the surface of each particle, and this Si functions as a deoxidizing element which suppresses the oxidation of Fe or Cr, and therefore, when the particles are sintered, the generation of a large amount of iron oxide or chromium oxide can be suppressed. As a result, the particles have more excellent sinterability and a sintered body having a higher density can be produced.

In the metal powder for powder metallurgy according to the aspect of the invention, it is preferred that the ratio of the content of 0 to the content of Si on the surface of each particle is 0.05 or more and 0.4 or less.

According to this, even if Si is segregated on the surface of each particle, the ratio of Si present in the form of silicon oxide can be sufficiently decreased. As a result, the deoxidizing effect of Si can be more reliably exhibited while suppressing the decrease in sinterability due to the presence of a large amount of silicon oxide.

In the metal powder for powder metallurgy according to the aspect of the invention, it is preferred that the content of Cr on the surface of each particle is lower than the content of Cr in the whole particle.

According to this, the excessive increase in the thickness of the passivation film formed on the surface of each particle can be suppressed, and therefore, the sinterability of the particle can be particularly enhanced.

In the metal powder for powder metallurgy according to the aspect of the invention, it is preferred that the ratio (X1/X2) of a value (X1) obtained by dividing the content (E1) of the first element by the mass number of the first element to a value (X2) obtained by dividing the content (E2) of the second element by the mass number of the second element is 0.3 or more and 3 or less.

According to this, the balance between the deposition amount of a carbide or the like of the first element and the deposition amount of a carbide or the like of the second element can be optimized. As a result, pores remaining in a molded body can be eliminated as if they were swept out sequentially from the inside, and therefore, pores generated in the sintered body can be minimized. Accordingly, a metal powder for powder metallurgy capable of producing a sintered body having a high density and excellent sintered body properties is obtained.

In the metal powder for powder metallurgy according to the aspect of the invention, it is preferred that the sum of the content of the first element and the content of the second element is 0.05% by mass or more and 0.8% by mass or less.

According to this, the densification of a sintered body to be produced becomes necessary and sufficient.

In the metal powder for powder metallurgy according to the aspect of the invention, it is preferred that the metal powder has an average particle diameter of 0.5 μm or more and 30 μm or less.

According to this, pores remaining in a sintered body are extremely decreased, and therefore, a sintered body having a particularly high density and particularly excellent mechanical properties can be produced.

A compound according to an aspect of the invention includes the metal powder for powder metallurgy according to the aspect of the invention and a binder which binds the particles of the metal powder for powder metallurgy to one another.

According to this, a compound capable of producing a sintered body having a high density is obtained.

A granulated powder according to an aspect of the invention is obtained by granulating the metal powder for powder metallurgy according to the aspect of the invention.

According to this, a granulated powder capable of producing a sintered body having a high density is obtained.

A sintered body according to an aspect of the invention is produced by sintering the metal powder for powder metallurgy according to the aspect of the invention.

According to this, a sintered body having a high density is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

FIG. 1 is a view schematically showing the cross sections of particles contained in an embodiment of a metal powder for powder metallurgy according to the invention.

FIG. 2 is an enlarged view of an area A of the cross section of the particle shown in FIG. 1 and is a view for illustrating a manner of performing an analysis in the depth direction by Auger electron spectroscopy in combination with sputtering of the surface of the particle.

FIG. 3 shows the Auger electron spectra obtained from a particle of a metal powder for powder metallurgy of sample No. 1.

FIG. 4 shows the Auger electron spectra obtained from a particle of a metal powder for powder metallurgy of sample No. 23.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a metal powder for powder metallurgy, a compound, a granulated powder, and a sintered body according to the invention will be described in detail with reference to preferred embodiments shown in the accompanying drawings.

Metal Powder for Powder Metallurgy

First, a metal powder for powder metallurgy according to the invention will be described.

In powder metallurgy, a sintered body having a desired shape can be obtained by molding a composition containing a metal powder for powder metallurgy and a binder into a desired shape, followed by degreasing and firing. According to such a powder metallurgy technique, an advantage that a sintered body with a complicated and fine shape can be produced in a near-net shape (a shape close to a final shape) as compared with the other metallurgy techniques is obtained.

With respect to the metal powder for powder metallurgy to be used in the powder metallurgy, an attempt to increase the density of a sintered body to be produced by appropriately changing the composition thereof has been made. However, in the sintered body, pores are liable to be generated, and therefore, in order to obtain mechanical properties comparable to those of ingot materials, it was necessary to further increase the density of the sintered body.

For example, in the past, the obtained sintered body was further subjected to an additional treatment such as a hot isostatic pressing treatment (HIP treatment) to increase the density. However, such an additional treatment requires much time, labor, and cost, and therefore becomes an obstacle to the expansion of the application of the sintered body.

In consideration of the above-mentioned problems, the present inventors have made intensive studies to find conditions for obtaining a sintered body having a high density without performing an additional treatment. As a result, they found that the density of a sintered body can be increased by optimizing the structure of each particle contained in a metal powder, and thus completed the invention.

Specifically, the metal powder for powder metallurgy according to this embodiment is a metal powder including particles, which contain Fe as a principal component, Cr in a proportion of 0.2% by mass or more and 35% by mass or less, Si in a proportion of 0.2% by mass or more and 3% by mass or less, C in a proportion of 0.005% by mass or more and 2% by mass or less, the below-mentioned first element in a proportion of 0.01% by mass or more and 0.5% by mass or less, and the below-mentioned second element in a proportion of 0.01% by mass or more and 0.5% by mass or less, wherein the content of Cr on the surface of each particle is 0.2% by atom or more and 15% by atom or less and is 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle. According to such a metal powder, as a result of optimizing the chemical composition and the particle structure, the densification during sintering can be particularly enhanced. As a result, a sintered body having a sufficiently high density can be produced without performing an additional treatment.

Such a sintered body has excellent mechanical properties. Due to this, the sintered body can be widely applied also to, for example, machine parts, structural parts, and the like, to which an external force is applied.

The first element is one element selected from the group consisting of the following seven elements: Ti, V, Y, Zr, Nb, Hf, and Ta, and the second element is one element selected from the group consisting of the above-mentioned seven elements and having a higher group number in the periodic table than that of the first element or one element selected from the group consisting of the above-mentioned seven elements and having the same group number in the periodic table as that of the element selected as the first element and a higher period number in the periodic table than that of the first element.

Hereinafter, the configuration of the metal powder for powder metallurgy according to this embodiment will be described in further detail. In the following description, the “metal powder for powder metallurgy” is sometimes simply referred to as “metal powder”, and each of the multiple particles constituting the metal powder for powder metallurgy is sometimes simply referred to as “particle”.

Structure of Particle

First, the structure of the particle of the metal powder for powder metallurgy according to this embodiment will be described.

FIG. 1 is a view schematically showing the cross sections of particles contained in the embodiment of a metal powder for powder metallurgy according to the invention, and FIG. 2 is an enlarged view of an area A of the cross section of the particle shown in FIG. 1 and is a view for illustrating a manner of performing an analysis in the depth direction by Auger electron spectroscopy in combination with sputtering of the surface of the particle.

When the content of Cr on the surface of a particle 1 is represented by Cr(0), and the content of Cr at a depth of 60 nm from the surface of the particle 1 is represented by Cr(60), the Cr(0) is 0.2% by atom or more and 15% by atom or less and is 70% or more and 170% or less the Cr(60).

It can be said that the particle 1 satisfying such conditions has a relatively fixed Cr content from the surface to the depth of 60 nm. Such a particle 1 has a passivation film derived from a Cr oxide whose thickness is small to some extent, and therefore, the decrease in the sinterability of the particle 1 due to the passivation film can be suppressed. As a result, the densification during sintering of the particles 1 is achieved, and therefore, a sintered body having a high density can be produced without performing an additional treatment.

When the Cr(0) is less than the above lower limit or the ratio of the Cr(0) to the Cr(60) is less than the above lower limit, the oxidation resistance on the surface of the particle 1 is deteriorated. If the oxidation resistance is deteriorated, the surface of the particle 1 is liable to be oxidized by the change in environment. At this time, the oxidation of the surface of the particle 1 is liable to occur unevenly among the particles 1, and therefore, the sinterability varies among the particles 1 resulting in deterioration of the densification of the sintered body. On the other hand, if the Cr(0) exceeds the above upper limit or the ratio of the Cr(0) to the Cr(60) exceeds the above upper limit, the thickness of the passivation film becomes too large. Therefore, the passivation film inhibits the sintering of the particles 1 resulting in deterioration of the densification of the sintered body.

The possibility that a region at a depth of 60 nm from the surface of the particle 1 contributes to sintering even when the metal powder is fired is considered to be low. In other words, the chemical composition at a depth of 60 nm is considered to be close to the chemical composition in the inside of the particle 1. Due to this, the fact that the Cr(0) is substantially the same as the Cr(60) means that a significantly thick passivation film is not formed on the surface of the particle 1, and this is considered to be the reason why the sinterability of the particle 1 is enhanced.

The Cr(0) and the Cr(60) can be obtained by an analysis in the depth direction by Auger electron spectroscopy in combination with sputtering. In this analysis, the particle 1 is irradiated with an electron beam while allowing ions to collide with the surface of the particle 1 to gradually strip an atomic layer, and atoms are identified and quantitatively determined based on the kinetic energy of Auger electrons emitted from the particle 1. Due to this, by converting a time required for sputtering into the thickness of the atomic layer stripped by the sputtering, the relationship between the depth from the surface of the particle 1 and the compositional ratio of the particle 1 can be obtained.

The relationship between the depth and the compositional ratio as described above can be obtained within the range of a depth of several hundred nanometers from the surface. At this time, it is only necessary that at least the Cr(0) and the Cr(60) satisfy the relationship described above, and for example, the content of Cr at a depth of 30 nm from the surface of the particle 1 may deviate from the range that the content is 70% or more and 170% or less the Cr(60).

The Cr(0) may be 0.2% by atom or more and 15% by atom or less, but is preferably set to 0.5% by atom or more and 13% by atom or less.

The Cr(0) may be 70% or more and 170% or less the Cr(60), but is preferably set to 80% or more and 150% or less the Cr(60).

Still further, when the content of Cr in the whole particle 1 is represented by Cr(w), the content of Cr on the surface of the particle 1 (Cr(0)) preferably satisfies the following relationship: Cr(0)<Cr(w), more preferably satisfies the following relationship: Cr(0)<0.8×Cr(w). By satisfying the relationship as described above, the content of Cr on the surface of the particle 1 can be made lower than the content of Cr in the whole particle 1. According to this, as compared with the thickness of the passivation film converted from the chemical composition of the whole particle 1, the thickness of the passivation film formed on the surface of the particle 1 can be prevented from excessively increasing, and therefore, the sinterability of the particle 1 can be particularly enhanced.

The content of Cr in the whole particle 1 can be determined by an analytical method described below.

Further, when the content of Si on the surface of the particle 1 is represented by Si(0), and the content of Si at a depth of 60 nm from the surface of the particle 1 is represented by Si(60), the Si(0) is preferably 155% or more and 800% or less, more preferably 200% or more and 500% or less the Si(60).

In the particle 1 satisfying such conditions, the content of Si on the surface is 1.55 times or more higher than the content of Si in the inside (at a depth of 60 nm). It can be said that in such a particle 1, Si is segregated on the surface. Si is considered to be present in the form of, for example, silicon oxide on the surface of the particle 1. Further, Si functions as a deoxidizing element which suppresses the oxidation of Fe or Cr, and therefore, the generation of iron oxide or chromium oxide on the surface of the particle 1 can be suppressed. Further, even in the case where oxygen is newly supplied when the particle 1 is sintered, the generation of a large amount of iron oxide or chromium oxide can be suppressed. As a result, the particle 1 has more excellent sinterability and a sintered body having a higher density can be produced.

Si present on the surface of the particle 1 functions to suppress the increase in the size of crystal grains when the metal powder is fired. Due to this, finer crystals are formed, and thus, a sintered body having excellent mechanical properties can be produced.

The Si(0) is preferably 15% by atom or more and 50% by atom or less, more preferably 25% by atom or more and 45% by atom or less.

The particle 1 satisfying such conditions can suppress the generation of a large amount of iron oxide or chromium oxide. Due to this, the particle 1 has more excellent sinterability and a sintered body having a higher density can be produced.

On the other hand, on the surface of the particle 1, Si is segregated, however, if a large amount of Si in the form of silicon oxide is present, in the same manner as iron oxide or chromium oxide, firing of the metal powder may be inhibited.

In view of this, when the content of 0 on the surface of the particle 1 is represented by O(0), the O(0) is preferably 0.05 times or more and 0.4 times or less, more preferably 0.1 times or more and 0.35 times or less the Si(0).

In the case where the ratio of O(0) to Si(0) falls within the above range, even if Si is segregated on the surface of the particle 1, the ratio of Si present in the form of silicon oxide is sufficiently decreased. Therefore, by making the ratio of O(0) to Si(0) fall within the above range, the deoxidizing effect of Si can be more reliably exhibited while suppressing the decrease in sinterability due to the presence of a large amount of silicon oxide. As a result, the particle 1 having particularly high sinterability is obtained, and by using the metal powder containing the particle 1, a sintered body having a high density can be produced.

The above-mentioned Si(0), Si(60), and O(0) can be also obtained by an analysis in the depth direction by Auger electron spectroscopy in combination with sputtering in the same manner as the Cr(0) and Cr(60).

By increasing the density of a sintered body in this manner, a sintered body having excellent mechanical properties is obtained. Such a sintered body can be widely applied also to, for example, machine parts, structural parts, and the like, to which an external force is applied.

Chemical Composition of Particle

Next, one example of the chemical composition of the whole particle 1 will be described.

Fe is a component (principal component) whose content is the highest in the chemical composition of the particle 1 and has a great influence on the properties of the sintered body. The content of Fe in the whole particle 1 is 50% by mass or more.

Cr

Cr (chromium) is an element which provides corrosion resistance to a sintered body to be produced. By using the metal powder containing Cr, a sintered body capable of maintaining high mechanical properties over a long period of time is obtained.

The content of Cr in the particle 1 is set to 0.2% by mass or more and 35% by mass or less, but is set to preferably 2% by mass or more and 32% by mass or less, more preferably 6% by mass or more and 30% by mass or less.

If the content of Cr is less than the above lower limit, the corrosion resistance of a sintered body to be produced may be insufficient depending on the overall composition. On the other hand, if the content of Cr exceeds the above upper limit, the sinterability is deteriorated depending on the overall composition so that it may become difficult to increase the density of the sintered body.

Ni

Ni (nickel) is an element which provides corrosion resistance and heat resistance to a sintered body to be produced as needed.

The content of Ni in the particle 1 is set to preferably 41% by mass or less, more preferably 10% by mass or more and 39% by mass or less, further more preferably 12% by mass or more and 27% by mass or less. By setting the content of Ni within the above range, a sintered body which maintains excellent mechanical properties over a long period of time can be obtained.

If the content of Ni is less than the above lower limit, the corrosion resistance and the heat resistance of a sintered body to be produced may not be sufficiently enhanced depending on the overall composition. On the other hand, if the content of Ni exceeds the above upper limit, the corrosion resistance and the heat resistance may be deteriorated instead.

In the case where Ni or Mo is contained in the particle 1, the content of Cr may be appropriately changed according to the content of Ni or Mo.

For example, in the case where the content of Ni is 7% by mass or more and 22% by mass or less and the content of Mo is less than 1.2% by mass, the content of Cr is more preferably 18% by mass or more and 20% by mass or less. On the other hand, in the case where the content of Ni is 10% by mass or more and 22% by mass or less and the content of Mo is 1.2% by mass or more and 5% by mass or less, the content of Cr is more preferably 16% by mass or more and less than 18% by mass.

Further, in the case where the content of Ni is 0.05% by mass or more and 0.6% by mass or less, the content of Cr is more preferably 10% by mass or more and 18% by mass or less.

Si

Si (silicon) is an element which provides corrosion resistance and high mechanical properties to a sintered body to be produced, and by using the metal powder containing Si, a sintered body capable of maintaining high mechanical properties over a long period of time can be obtained.

The content of Si in the metal powder is set to 0.2% by mass or more and 3% by mass or less, but is set to preferably 0.4% by mass or more and 1.5% by mass or less, more preferably 0.5% by mass or more and 1% by mass or less.

If the content of Si is less than the above lower limit, the effect of the addition of Si is weakened depending on the overall composition so that the corrosion resistance and the mechanical properties of a sintered body to be produced may be deteriorated. On the other hand, if the content of Si exceeds the above upper limit, the amount of Si is too large depending on the overall composition so that the corrosion resistance and the mechanical properties may be deteriorated instead.

C

By using C (carbon) in combination with the first element and the second element, a carbide or the like of the first element and a carbide or the like of the second element are generated as described above. According to this, a sintered body having a high density can be obtained as described above.

The content of C in the particle 1 is set to 0.005% by mass or more and 2% by mass or less, but is set to preferably 0.01% by mass or more and 1.5% by mass or less, more preferably 0.02% by mass or more and 1% by mass or less.

If the content of C is less than the above lower limit, it is difficult to generate sufficient amounts of a carbide or the like of the first element and a carbide or the like of the second element depending on the overall composition, and therefore, the densification of the sintered body may be insufficient. On the other hand, if the content of C exceeds the above upper limit, the amount of C with respect to the amounts of the first element and the second element is too large depending on the overall composition, and therefore, the sinterability of the particle 1 may be deteriorated instead.

In the case where Ni is contained in the particle 1, the content of C may be appropriately changed according to the content of Ni.

For example, in the case where the content of Ni is 7% by mass or more and 22% by mass or less, the content of C is more preferably 0.005% by mass or more and 0.3% by mass or less.

Further, in the case where the content of Ni is 0.05% by mass or more and 0.6% by mass or less, the content of C is more preferably 0.15% by mass or more and 1.2% by mass or less.

In the case where Ni is contained in the particle 1, the content of Ni is preferably set to 0.05% by mass or more and 22% by mass or less. By adding Ni to the particle 1, the corrosion resistance and the heat resistance of a sintered body to be produced can be further enhanced.

If the content of Ni is less than the above lower limit, the corrosion resistance and the heat resistance of a sintered body to be produced may not be sufficiently enhanced depending on the overall composition. On the other hand, if the content of Ni exceeds the above upper limit, the corrosion resistance and the heat resistance may be deteriorated instead.

First Element and Second Element

The first element and the second element each deposit a carbide or an oxide (hereinafter also collectively referred to as “carbide or the like”). It is considered that this deposited carbide or the like inhibits the significant growth of crystal grains when the metal powder is sintered. As a result, as described above, it becomes difficult to generate pores in a sintered body, and also the increase in the size of crystal grains is prevented, and thus, a sintered body having a high density and excellent mechanical properties is obtained.

In addition, although a detailed description will be given later, the deposited carbide or the like promotes the accumulation of silicon oxide at a crystal grain boundary, and as a result, the sintering is promoted and the density is increased while preventing the increase in the size of crystal grains.

The first element and the second element are two elements selected from the group consisting of the following seven elements: Ti, V, Y, Zr, Nb, Hf, and Ta, but preferably include an element belonging to group IIIA or group IVA in the long periodic table (Ti, Y, Zr, or Hf). By including an element belonging to group IIIA or group IVA as at least one of the first element and the second element, oxygen contained as an oxide in the metal powder is removed and the sinterability of the metal powder can be particularly enhanced.

The first element is only required to be one element selected from the group consisting of the following seven elements: Ti, V, Y, Zr, Nb, Hf, and Ta as described above, but is preferably an element belonging to group IIIA or group IVA in the long periodic table in the group consisting of the above-mentioned seven elements. An element belonging to group IIIA or group IVA removes oxygen contained as an oxide in the metal powder (functions as a deoxidizing element) and therefore can particularly enhance the sinterability of the metal powder. According to this, the concentration of oxygen remaining in the crystal grains after sintering can be decreased. As a result, the content of oxygen in the sintered body can be decreased, and the density can be increased. Further, these elements are elements having high activity, and therefore are considered to cause rapid atomic diffusion. Accordingly, this atomic diffusion acts as a driving force, and thereby a distance between particles of the metal powder is efficiently decreased and a neck is formed between the particles, so that the densification of a molded body is promoted. As a result, the density of the sintered body can be further increased.

On the other hand, the second element is only required to be one element selected from the group consisting of the following seven elements: Ti, V, Y, Zr, Nb, Hf, and Ta and different from the first element as described above, but is preferably an element belonging to group VA in the long periodic table in the group consisting of the above-mentioned seven elements. An element belonging to group V A particularly efficiently deposits the above-mentioned carbide or the like, and therefore, can efficiently inhibit the significant growth of crystal grains during sintering. As a result, the formation of fine crystal grains is promoted, and thus, the density of the sintered body can be increased and also the mechanical properties of the sintered body can be enhanced.

Incidentally, by the combination of the first element with the second element composed of the elements as described above, the effects of the respective elements are exhibited without inhibiting each other. Due to this, the metal powder containing such a first element and a second element enables the production of a sintered body having a particularly high density.

More preferably, a combination of an element belonging to group IVA as the first element with Nb as the second element is adopted.

Further, more preferably, a combination of Zr or Hf as the first element with Nb as the second element is adopted.

By adopting such a combination, the above-mentioned effect becomes more prominent.

In the case where the first element is particularly Zr, Zr is a ferrite forming element, and therefore deposits a body-centered cubic lattice phase. This body-centered cubic lattice phase has more excellent sinterability than the other crystal lattice phases, and therefore contributes to the densification of a sintered body.

The atomic radius of Zr is slightly larger than that of Fe. Specifically, the atomic radius of Fe is about 0.117 nm, and the atomic radius of Zr is about 0.145 nm. Therefore, Zr is solid-dissolved in Fe, but is not completely solid-dissolved therein, and part of Zr is deposited as a carbide or the like. According to this, an appropriate amount of a carbide or the like is deposited, and therefore, the increase in the size of crystal grains can be effectively prevented while promoting the sintering and increasing the density.

In the case where the second element is particularly Nb, the atomic radius of Nb is slightly larger than that of Fe, but slightly smaller than that of Zr. Specifically, the atomic radius of Fe is about 0.117 nm, and the atomic radius of Nb is about 0.134 nm. Therefore, Nb is solid-dissolved in Fe, but is not completely solid-dissolved therein, and part of Nb is deposited as a carbide or the like. According to this, an appropriate amount of a carbide or the like is deposited, and therefore, the increase in the size of crystal grains can be effectively prevented while promoting the sintering and increasing the density.

The content of the first element in the metal powder is set to 0.01% by mass or more and 0.5% by mass or less, but is set to preferably 0.03% by mass or more and 0.4% by mass or less, more preferably 0.05% by mass or more and 0.3% by mass or less. If the content of the first element is less than the above lower limit, the effect of the addition of the first element is weakened depending on the overall composition so that the density of a sintered body to be produced is not sufficiently increased. On the other hand, if the content of the first element exceeds the above upper limit, the amount of the first element is too large depending on the overall composition so that the ratio of the above-mentioned carbide or the like is too high, and therefore, the densification is deteriorated instead.

The content of the second element in the metal powder is set to 0.01% by mass or more and 0.5% by mass or less, but is set to preferably 0.03% by mass or more and 0.4% by mass or less, more preferably 0.05% by mass or more and 0.3% by mass or less. If the content of the second element is less than the above lower limit, the effect of the addition of the second element is weakened depending on the overall composition so that the density of a sintered body to be produced is not sufficiently increased. On the other hand, if the content of the second element exceeds the above upper limit, the amount of the second element is too large depending on the overall composition so that the ratio of the above-mentioned carbide or the like is too high, and therefore, the densification is deteriorated instead.

Further, as described above, each of the first element and the second element deposits a carbide or the like, however, in the case where an element belonging to group III A or group IVA is selected as the first element as described above and an element belonging to group VA is selected as the second element as described above, it is presumed that when the metal powder is sintered, the timing when a carbide or the like of the first element is deposited and the timing when a carbide or the like of the second element is deposited differ moderately from each other. It is considered that due to the difference in timing when a carbide or the like is deposited in this manner, sintering gradually proceeds so that the generation of pores is prevented, and thus, a dense sintered body is obtained. That is, it is considered that by the presence of both of the carbide or the like of the first element and the carbide or the like of the second element, the increase in the size of crystal grains can be suppressed while increasing the density of the sintered body.

Due to such a difference in timing, the carbide or the like of the first element and the carbide or the like of the second element deposited in the particle 1 are mutually exclusively present. That is, the carbide or the like of the first element and the carbide or the like of the second element are less likely to be deposited at the same site, and most of them are deposited apart from each other. Then, by the presence of both of the carbide or the like of the first element and the carbide or the like of the second element in this manner, when the particles 1 are sintered, the increase in the size of crystal grains is more reliably prevented, and thus, the density of the sintered body can be increased.

Further, since the carbide or the like of the first element and the carbide or the like of the second element are deposited apart from each other, an effect of preventing the increase in the size of crystal grains is uniformly exhibited in the particle 1. In view of this, the densification of the sintered body is particularly promoted.

In addition, it is considered that in the particle 1, the carbide or the like of the first element and the carbide or the like of the second element act as “nuclei”, and the accumulation of silicon oxide occurs. By the accumulation of silicon oxide at a crystal grain boundary, the concentration of oxides inside the crystal is decreased, and therefore, sintering is promoted. As a result, it is considered that the densification of the sintered body is further promoted when the particles 1 are sintered.

When such particles 1 are subjected to powder metallurgy, a sintered body can be densified, and therefore, a sintered body having a high density can be produced without performing an additional treatment. It is considered that when the particles 1 are subjected to powder metallurgy, the carbide or the like moves to a metal crystal grain boundary in a sintered body. Then, the carbide or the like having moved to the triple point of a crystal grain boundary suppresses the crystal growth at this point (a flux pinning effect). As a result, the significant growth of crystal grains is suppressed, and thus, a sintered body having finer crystals is obtained. Such a sintered body has particularly high mechanical properties.

Further, it is preferred to set the ratio of the content of the first element to the content of the second element in consideration of the mass number of the first element and the mass number of the second element.

Specifically, when a value obtained by dividing the content E1 (mass %) of the first element by the mass number of the first element is represented by X1 and a value obtained by dividing the content E2 (mass %) of the second element by the mass number of the second element is represented by X2, X1/X2 is preferably 0.3 or more and 3 or less, more preferably 0.5 or more and 2 or less, further more preferably 0.75 or more and 1.3 or less. By setting the ratio X1/X2 within the above range, the balance between the deposition amount of the carbide or the like of the first element and the deposition amount of the carbide or the like of the second element can be optimized. According to this, pores remaining in a molded body can be eliminated as if they were swept out sequentially from the inside, and therefore, pores generated in a sintered body can be minimized. Accordingly, a metal powder capable of producing a sintered body having a high density and excellent mechanical properties can be obtained by setting the ratio X1/X2 within the above range.

Here, with respect to a specific example of the combination of the first element with the second element, based on the above-mentioned range of the ratio X1/X2, the ratio (E1/E2) of the content E1 of the first element to the content E2 of the second element is calculated.

For example, in the case where the first element is Zr and the second element is Nb, since the mass number of Zr is 91.2 and the mass number of Nb is 92.9, E1/E2 is preferably 0.29 or more and 2.95 or less, more preferably 0.49 or more and 1.96 or less.

In the case where the first element is Hf and the second element is Nb, since the mass number of Hf is 178.5 and the mass number of Nb is 92.9, E1/E2 is preferably 0.58 or more and 5.76 or less, more preferably 0.96 or more and 3.84 or less.

In the case where the first element is Ti and the second element is Nb, since the mass number of Ti is 47.9 and the mass number of Nb is 92.9, E1/E2 is preferably 0.15 or more and 1.55 or less, more preferably 0.26 or more and 1.03 or less.

In the case where the first element is Nb and the second element is Ta, since the mass number of Nb is 92.9 and the mass number of Ta is 180.9, E1/E2 is preferably 0.15 or more and 1.54 or less, more preferably 0.26 or more and 1.03 or less.

In the case where the first element is Y and the second element is Nb, since the mass number of Y is 88.9 and the mass number of Nb is 92.9, E1/E2 is preferably 0.29 or more and 2.87 or less, more preferably 0.48 or more and 1.91 or less.

In the case where the first element is V and the second element is Nb, since the mass number of V is 50.9 and the mass number of Nb is 92.9, E1/E2 is preferably 0.16 or more and 1.64 or less, more preferably 0.27 or more and 1.10 or less.

In the case where the first element is Ti and the second element is Zr, since the mass number of Ti is 47.9 and the mass number of Zr is 91.2, E1/E2 is preferably 0.16 or more and 1.58 or less, more preferably 0.26 or more and 1.05 or less.

In the case where the first element is Zr and the second element is Ta, since the mass number of Zr is 91.2 and the mass number of Ta is 180.9, E1/E2 is preferably 0.15 or more and 1.51 or less, more preferably 0.25 or more and 1.01 or less.

In the case where the first element is Zr and the second element is V, since the mass number of Zr is 91.2 and the mass number of V is 50.9, E1/E2 is preferably 0.54 or more and 5.38 or less, more preferably 0.90 or more and 3.58 or less.

Also in the case of a combination other than the above-mentioned combinations, E1/E2 can be calculated in the same manner as described above.

The sum of the content E1 of the first element and the content E2 of the second element is preferably 0.05% by mass or more and 0.8% by mass or less, more preferably 0.10% by mass or more and 0.6% by mass or less, further more preferably 0.12% by mass or more and 0.24% by mass or less. By setting the sum of the content of the first element and the content of the second element within the above range, the densification of a sintered body to be produced becomes necessary and sufficient.

When the ratio of the sum of the content of the first element and the content of the second element to the content of Si is represented by (E1+E2)/Si, (E1+E2)/Si is preferably 0.1 or more and 0.7 or less, more preferably 0.15 or more and 0.6 or less, further more preferably 0.2 or more and 0.5 or less in terms of mass ratio. By setting the ratio (E1+E2)/Si within the above range, a decrease in the toughness or the like when Si is added is sufficiently compensated by the addition of the first element and the second element. As a result, a metal powder capable of producing a sintered body which has excellent mechanical properties such as toughness in spite of having a high density and also has excellent corrosion resistance attributed to Si is obtained. In addition, in the particle 1, necessary and sufficient accumulation of silicon oxide occurs by using the carbide or the like of the first element and the carbide or the like of the second element as nuclei, and in the case where an element such as Ni is contained in the particle 1 other than Fe and Cr, an oxidation reaction of such an element is easily suppressed. Therefore, also from this viewpoint, the sinterability of the particle 1 is enhanced, and thus, a sintered body having a higher density, excellent mechanical properties, and excellent corrosion resistance can be obtained.

Further, when the ratio of the sum of the content of the first element and the content of the second element to the content of C is represented by (E1+E2)/C, (E1+E2)/C is preferably 1 or more and 16 or less, more preferably 2 or more and 13 or less, further more preferably 3 or more and 10 or less. By setting the ratio (E1+E2)/C within the above range, an increase in the hardness and the suppression of a decrease in the toughness when C is added, and an increase in the density brought about by the addition of the first element and the second element can be achieved. As a result, the particle 1 capable of producing a sintered body which has excellent mechanical properties such as tensile strength and toughness is obtained.

The metal powder is only required to contain two elements selected from the group consisting of the above-mentioned seven elements, but may further contain an element which is selected from this group and is different from these two elements. That is, the metal powder may contain three or more elements selected from the group consisting of the above-mentioned seven elements. According to this, the above-mentioned effect can be further enhanced, which slightly varies depending on the combination of the elements to be contained.

Another Element

The particle 1 may contain, other than the above-mentioned elements, at least one element of W, Co, Mn, Mo, Cu, N, and S as needed. These elements may be inevitably contained in some cases.

W is an element which enhances the heat resistance of a sintered body to be produced.

The content of W in the particle 1 is set to 0.5% by mass or more and 20% by mass or less, but is set to preferably 1% by mass or more and 10% by mass or less, more preferably 5% by mass or more and 7% by mass or less. If the content of W is less than the above lower limit, the heat resistance and the sintered body cannot be sufficiently enhanced depending on the overall composition, and for example, when a tool is produced by using the obtained sintered body, the hardness, softening resistance, and abrasion resistance of the tool at a high temperature may be deteriorated. On the other hand, if the content of W exceeds the above upper limit, the mechanical properties such as toughness of the sintered body may be deteriorated depending on the overall composition, and for example, a problem such as a chipping may occur in the tool.

Co is an element which enhances the heat resistance of a sintered body to be produced.

The content of Co in the particle 1 is not particularly limited, but is preferably 3% by mass or more and 12% by mass or less, more preferably 4.5% by mass or more and 10.5% by mass or less. By setting the content of Co within the above range, the heat resistance of a sintered body to be produced can be further enhanced without causing a large decrease in the density of the sintered body. In particular, the decrease in the hardness or the softness resistance at a high temperature can be suppressed, and therefore, for example, when a tool is produced by using the obtained sintered body, a high-speed tool which can be cut at a higher speed can be easily produced.

Mn is an element which provides corrosion resistance and high mechanical properties to a sintered body to be produced.

The content of Mn in the particle 1 is not particularly limited, but is preferably 0.01% by mass or more and 3% by mass or less, more preferably 0.05% by mass or more and 1% by mass or less. By setting the content of Mn within the above range, a sintered body having a higher density and excellent mechanical properties is obtained.

If the content of Mn is less than the above lower limit, the corrosion resistance and the mechanical properties of a sintered body to be produced may not be sufficiently enhanced depending on the overall composition. On the other hand, if the content of Mn exceeds the above upper limit, the corrosion resistance and the mechanical properties may be deteriorated instead depending on the overall composition.

Mo is an element which enhances the corrosion resistance of a sintered body to be produced.

The content of Mo in the particle 1 is not particularly limited, but is preferably 1% by mass or more and 5% by mass or less, more preferably 1.2% by mass or more and 4% by mass or less, further more preferably 2% by mass or more and 3% by mass or less. By setting the content of Mo within the above range, the corrosion resistance of a sintered body to be produced can be further enhanced without causing a large decrease in the density of the sintered body.

Cu is an element which enhances the corrosion resistance of a sintered body to be produced.

The content of Cu in the particle 1 is not particularly limited, but is preferably 5% by mass or less, more preferably 1% by mass or more and 4% by mass or less. By setting the content of Cu within the above range, the corrosion resistance of a sintered body to be produced can be further enhanced without causing a large decrease in the density of the sintered body.

In the case where the content of Ni is 0.05% by mass or more and 0.6% by mass or less, the content of Cu is preferably less than 1% by mass or less, more preferably less than 0.1% by mass or less. Further, in this case, it is more preferred that the particle 1 substantially contains no Cu (the content of Cu is set to less than 0.01% by mass) excluding the amount of Cu which is inevitably contained. The detailed reasons therefor have not been known, however, this is due to the fear that by the incorporation of Cu, the effect brought about by the first element and the second element as described above may be weakened.

N is an element which enhances the mechanical properties such as proof stress of a sintered body to be produced.

The content of N in the particle 1 is not particularly limited, but is preferably 0.03% by mass or more and 1% by mass or less, more preferably 0.08% by mass or more and 0.3% by mass or less, further more preferably 0.1% by mass or more and 0.25% by mass or less. By setting the content of N within the above range, the mechanical properties such as proof stress of a sintered body to be produced can be further enhanced without causing a large decrease in the density of the sintered body.

In order to produce the particles 1 to which N is added, for example, a method using a nitrided starting material, a method of introducing nitrogen gas into a molten metal, a method of performing a nitriding treatment of a produced metal powder, or the like is used.

S is an element which enhances the machinability of a sintered body to be produced.

The content of S in the particle 1 is not particularly limited, but is preferably 0.5% by mass or less, more preferably 0.01% by mass or more and 0.3% by mass or less. By setting the content of S within the above range, the machinability of a sintered body to be produced can be further enhanced without causing a large decrease in the density of the sintered body. Accordingly, the obtained sintered body can be cut out into a desired shape by performing a machining process.

To the particle 1, B, Se, Te, Pd, Al, or the like may be added other than the above-mentioned elements. At this time, the contents of these elements are not particularly limited, but the content of each element is preferably less than 0.1% by mass, and also the total content of these elements is preferably less than 0.2% by mass. These elements may be inevitably contained in some cases.

The particle 1 may contain impurities. Examples of the impurities include all elements other than the above-mentioned elements, and examples thereof include Li, Be, Na, Mg, P, K, Ca, Sc, Zn, Ga, Ge, Ag, In, Sn, Sb, Os, Ir, Pt, Au, and Bi. The incorporation amounts of these impurity elements are preferably such that the content of each of the impurity elements is less than the content of each of the above-mentioned constituent elements of the particle 1. Further, the incorporation amount of these impurity elements is preferably set such that the content of each of the impurity elements is less than 0.03% by mass, more preferably less than 0.02% by mass. Further, the total content of these impurity elements is set to preferably less than 0.3% by mass, more preferably less than 0.2% by mass. These elements do not inhibit the effect as described above as long as the contents thereof are within the above range, and therefore may be intentionally added to the particle 1.

Meanwhile, O (oxygen) may also be intentionally added to or inevitably mixed in the metal powder, however, the amount thereof is preferably about 0.8% by mass or less, more preferably about 0.5% by mass or less. By controlling the amount of oxygen in the metal powder within the above range, the sinterability is enhanced, and thus, a sintered body having a high density and excellent mechanical properties is obtained. Incidentally, the lower limit thereof is not particularly set, but is preferably 0.03% by mass or more from the viewpoint of ease of mass production or the like.

The chemical composition of the particle 1 can be determined by, for example, Iron and steel—Atomic absorption spectrometric method specified in JIS G 1257 (2000), Iron and steel—ICP atomic emission spectrometric method specified in JIS G 1258 (2007), Iron and steel—Method for spark discharge atomic emission spectrometric analysis specified in JIS G 1253 (2002), Iron and steel—Method for X-ray fluorescence spectrometric analysis specified in JIS G 1256 (1997), gravimetric, titrimetric, and absorption spectrometric methods specified in JIS G 1211 to G 1237, or the like. Specifically, for example, an optical emission spectrometer for solids (spark optical emission spectrometer, model: SPECTROLAB, type: LAVMB08A) manufactured by SPECTRO Analytical Instruments GmbH or an ICP device (model: CIROS-120) manufactured by Rigaku Corporation can be used.

Incidentally, the methods specified in JIS G 1211 to G 1237 are as follows.

JIS G 1211 (2011): Iron and steel—Methods for determination of carbon content

JIS G 1212 (1997): Iron and steel—Methods for determination of silicon content

JIS G 1213 (2001): Iron and steel—Methods for determination of manganese content

JIS G 1214 (1998): Iron and steel—Methods for determination of phosphorus content

JIS G 1215 (2010): Iron and steel—Methods for determination of sulfur content

JIS G 1216 (1997): Iron and steel—Methods for determination of nickel content

JIS G 1217 (2005): Iron and steel—Methods for determination of chromium content

JIS G 1218 (1999): Iron and steel—Methods for determination of molybdenum content

JIS G 1219 (1997): Iron and steel—Methods for determination of copper content

JIS G 1220 (1994): Iron and steel—Methods for determination of tungsten content

JIS G 1221 (1998): Iron and steel—Methods for determination of vanadium content

JIS G 1222 (1999): Iron and steel—Methods for determination of cobalt content

JIS G 1223 (1997): Iron and steel—Methods for determination of titanium content

JIS G 1224 (2001): Iron and steel—Methods for determination of aluminum content

JIS G 1225 (2006): Iron and steel—Methods for determination of arsenic content

JIS G 1226 (1994): Iron and steel—Methods for determination of tin content

JIS G 1227 (1999): Iron and steel—Methods for determination of boron content

JIS G 1228 (2006): Iron and steel—Methods for determination of nitrogen content

JIS G 1229 (1994): Steel—Methods for determination of lead content

JIS G 1232 (1980): Methods for determination of zirconium in steel

JIS G 1233 (1994): Steel—Method for determination of selenium content

JIS G 1234 (1981): Methods for determination of tellurium in steel

JIS G 1235 (1981): Methods for determination of antimony in iron and steel

JIS G 1236 (1992): Method for determination of tantalum in steel

JIS G 1237 (1997): Iron and steel—Methods for determination of niobium content

Further, when C (carbon) and S (sulfur) are determined, particularly, an infrared absorption method after combustion in a current of oxygen (after combustion in a high-frequency induction heating furnace) specified in JIS G 1211 (2011) is also used. Specifically, a carbon-sulfur analyzer, CS-200 manufactured by LECO Corporation can be used.

Further, when N (nitrogen) and O (oxygen) are determined, particularly, a method for determination of nitrogen content in iron and steel specified in JIS G 1228 (2006) and a method for determination of oxygen content in metallic materials specified in JIS Z 2613 (2006) are also used. Specifically, an oxygen-nitrogen analyzer, TC-300/EF-300 manufactured by LECO Corporation can be used.

Further, the particle 1 as described above is preferably contained in the metal powder for powder metallurgy as much as possible, and specifically, the particle 1 is contained therein in an amount of preferably 50% by number or more, more preferably 60% by number or more. According to such a metal powder for powder metallurgy, the effect as described above brought about by the particle 1 is more reliably exhibited.

The above-mentioned ratio can be obtained by arbitrarily extracting 20 or more particles in the metal powder for powder metallurgy and counting the particles 1 as described above.

The average particle diameter of the metal powder for powder metallurgy of the invention is preferably 0.5 μm or more and 30 μm or less, more preferably 1 μm or more and 20 μn or less, further more preferably 2 μn or more and 10 μn or less. By using the metal powder for powder metallurgy having such a particle diameter, pores remaining in a sintered body are extremely reduced, and therefore, a sintered body having a particularly high density and particularly excellent mechanical properties can be produced.

The average particle diameter can be obtained as a particle diameter when the cumulative amount obtained by cumulating the percentages of the particles from the smaller diameter side reaches 50% in a cumulative particle size distribution on amass basis obtained by laser diffractometry.

If the average particle diameter of the metal powder for powder metallurgy is less than the above lower limit, the moldability is deteriorated in the case where the shape is difficult to mold, and therefore, the sintered density may be decreased. On the other hand, if the average particle diameter of the metal powder exceeds the above upper limit, spaces between the particles become larger during molding, and therefore, the sintered density may be decreased also in this case.

The particle size distribution of the metal powder for powder metallurgy is preferably as narrow as possible. Specifically, when the average particle diameter of the metal powder for powder metallurgy is within the above range, the maximum particle diameter of the metal powder is preferably 200 μm or less, more preferably 150 μm or less. By controlling the maximum particle diameter of the metal powder for powder metallurgy within the above range, the particle size distribution of the metal powder for powder metallurgy can be made narrower, and thus, the density of the sintered body can be further increased.

Here, the “maximum particle diameter” refers to a particle diameter when the cumulative amount obtained by cumulating the percentages of the particles from the smaller diameter side reaches 99.9% in a cumulative particle size distribution on amass basis obtained by laser diffractometry.

When the minor axis of each particle of the metal powder for powder metallurgy is represented by S (μm) and the major axis thereof is represented by L (μm), the average of the aspect ratio defined by S/L is preferably about 0.4 or more and 1 or less, more preferably about 0.7 or more and 1 or less. The metal powder for powder metallurgy having an aspect ratio within this range has a shape relatively close to a spherical shape, and therefore, the packing factor when the metal powder is molded is increased. As a result, the density of the sintered body can be further increased.

Here, the “major axis” is the maximum length in the projected image of the particle, and the “minor axis” is the maximum length in the direction perpendicular to the major axis. Incidentally, the average of the aspect ratio can be obtained as the average of the measured aspect ratios of 100 or more particles.

The tap density of the metal powder for powder metallurgy of the invention is preferably 3.5 g/cm³ or more, more preferably 4 g/cm³ or more. According to the metal powder for powder metallurgy having such a high tap density, when a molded body is obtained, the interparticle packing efficiency is particularly increased. Therefore, a particularly dense sintered body can be obtained in the end.

The specific surface area of the metal powder for powder metallurgy of the invention is not particularly limited, but is preferably 0.1 m²/g or more, more preferably 0.2 m²/g or more. According to the metal powder for powder metallurgy having such a large specific surface area, a surface activity (surface energy) is increased so that it is possible to easily sinter the metal powder even if less energy is applied. Therefore, when a molded body is sintered, a difference in sintering rate hardly occurs between the inner side and the outer side of the molded body, and thus, the decrease in the sintered density due to the pores remaining inside the molded body can be suppressed.

Method for Producing Sintered Body

Next, a method for producing a sintered body using such a metal powder for powder metallurgy according to the invention will be described.

The method for producing a sintered body includes (A) a composition preparation step in which a composition for producing a sintered body is prepared, (B) a molding step in which a molded body is produced, (C) a degreasing step in which a degreasing treatment is performed, and (D) a firing step in which firing is performed. Hereinafter, the respective steps will be described sequentially.

(A) Composition Preparation Step

First, the metal powder for powder metallurgy according to the invention and a binder are prepared, and these materials are kneaded using a kneader, whereby a kneaded material (composition) is obtained.

In this kneaded material (an embodiment of the compound according to the invention), the metal powder for powder metallurgy is uniformly dispersed.

The metal powder for powder metallurgy according to the invention is produced by, for example, any of a variety of powdering methods such as an atomization method (such as a water atomization method, a gas atomization method, or a spinning water atomization method), a reducing method, a carbonyl method, and a pulverization method.

Among these, the metal powder for powder metallurgy according to the invention is preferably a metal powder produced by an atomization method, more preferably a metal powder produced by a water atomization method or a spinning water atomization method. The atomization method is a method in which a molten metal (metal melt) is caused to collide with a fluid (liquid or gas) sprayed at a high speed to atomize the metal melt into a fine powder and also to cool the fine powder, whereby a metal powder is produced. By producing the metal powder for powder metallurgy through such an atomization method, an extremely fine powder can be efficiently produced. Further, the shape of the particle of the obtained powder is closer to a spherical shape by the action of surface tension. Due to this, when the metal powder is molded, a molded body having a high packing factor is obtained. That is, a powder capable of producing a sintered body having a high density can be obtained. In addition, the cooling rate of the metal melt is very high, and therefore, the particle 1 in which the second region P2 and the third region P3 are more uniformly distributed can be obtained.

In the case where a water atomization method is used as the atomization method, the pressure of water (hereinafter referred to as “atomization water”) to be sprayed to the molten metal is not particularly limited, but is set to preferably about 75 MPa or more and 120 MPa or less (750 kgf/cm² or more and 1200 kgf/cm² or less), more preferably about 90 MPa or more and 120 MPa or less (900 kgf/cm² or more and 1200 kgf/cm² or less).

The temperature of the atomization water is also not particularly limited, but is preferably set to about 1° C. or higher and 20° C. or lower.

The atomization water is often sprayed in a cone shape such that it has a vertex on the falling path of the metal melt and the outer diameter gradually decreases downward. In this case, the vertex angle θ of the cone formed by the atomization water is preferably about 10° or more and 40° or less, more preferably about 15° or more and 35° or less. According to this, a metal powder for powder metallurgy having a composition as described above can be reliably produced.

Further, by using a water atomization method (particularly, a spinning water atomization method), the metal melt can be cooled particularly quickly. Due to this, a powder having high quality can be obtained in a wide alloy composition range.

The cooling rate when cooling the metal melt in the atomization method is preferably 1×10⁴° C./s or more, more preferably 1×10⁵° C./s or more. By the quick cooling in this manner, a homogeneous metal powder for powder metallurgy can be obtained. As a result, a sintered body having high quality can be obtained. Incidentally, the volume occupancy of the crystalline material as described above in the particle 1 varies depending on the conditions (for example, the alloy composition, the production conditions, etc.) when the metal powder for powder metallurgy is produced. For example, in the case where the cooling rate is increased (for example, in the case of 1×10⁵° C./s or more), the volume of an amorphous material or a metal glass tends to slightly increase, and in the case where the cooling rate is decreased (for example, in the case of 1×10⁴° C./s or more and less than 1×10⁵° C./s), the volume of a crystalline material tends to slightly increase.

The thus obtained metal powder for powder metallurgy may be classified as needed. Examples of the classification method include dry classification such as sieving classification, inertial classification, and centrifugal classification, and wet classification such as sedimentation classification.

Examples of the binder include polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrenic resins such as polystyrene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, and polybutylene terephthalate, various resins such as polyether, polyvinyl alcohol, polyvinylpyrrolidone, and copolymers thereof, and various organic binders such as various waxes, paraffins, higher fatty acids (such as stearic acid), higher alcohols, higher fatty acid esters, and higher fatty acid amides. These can be used alone or by mixing two or more types thereof.

The content of the binder is preferably about 2% by mass or more and 20% by mass or less, more preferably about 5% by mass or more and 10% by mass or less with respect to the total amount of the kneaded material. By setting the content of the binder within the above range, a molded body can be formed with good moldability, and also the density is increased, whereby the stability of the shape of the molded body and the like can be particularly enhanced. Further, according to this, a difference in size between the molded body and the degreased body, that is, so-called a shrinkage ratio is optimized, whereby a decrease in the dimensional accuracy of the finally obtained sintered body can be prevented. That is, a sintered body having a high density and high dimensional accuracy can be obtained.

In the kneaded material, a plasticizer may be added as needed. Examples of the plasticizer include phthalate esters (such as DOP, DEP, and DBP), adipate esters, trimellitate esters, and sebacate esters. These can be used alone or by mixing two or more types thereof.

Further, in the kneaded material, other than the metal powder for powder metallurgy, the binder, and the plasticizer, for example, any of a variety of additives such as a lubricant, an antioxidant, a degreasing accelerator, and a surfactant can be added as needed.

The kneading conditions vary depending on the respective conditions such as the metal composition or the particle diameter of the metal powder for powder metallurgy to be used, the composition of the binder, and the blending amount thereof. However, for example, the kneading temperature can be set to about 50° C. or higher and 200° C. or lower, and the kneading time can be set to about 15 minutes or more and 210 minutes or less.

Further, the kneaded material is formed into a pellet (small particle) as needed. The particle diameter of the pellet is set to, for example, about 1 mm or more and 15 mm or less.

Incidentally, depending on the molding method described below, in place of the kneaded material, a granulated powder may be produced. The kneaded material, the granulated powder, and the like are examples of the composition to be subjected to the molding step described below.

The embodiment of the granulated powder according to the invention is directed to a granulated powder obtained by binding a plurality of metal particles to one another with a binder by subjecting the metal powder for powder metallurgy according to the invention to a granulation treatment.

Examples of the binder to be used for producing the granulated powder include polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrenic resins such as polystyrene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, and polybutylene terephthalate, various resins such as polyether, polyvinyl alcohol, polyvinylpyrrolidone, and copolymers thereof, and various organic binders such as various waxes, paraffins, higher fatty acids (such as stearic acid), higher alcohols, higher fatty acid esters, and higher fatty acid amides. These can be used alone or by mixing two or more types thereof.

Among these, as the binder, a binder containing a polyvinyl alcohol or polyvinylpyrrolidone is preferred. These binder components have a high binding ability, and therefore can efficiently form the granulated powder even in a relatively small amount. Further, the thermal decomposability thereof is also high, and therefore, the binder can be reliably decomposed and removed in a short time during degreasing and firing.

The content of the binder is preferably about 0.2% by mass or more and 10% by mass or less, more preferably about 0.3% by mass or more and 5% by mass or less, further more preferably about 0.3% by mass or more and 2% by mass or less with respect to the total amount of the granulated powder. By setting the content of the binder within the above range, the granulated powder can be efficiently formed while preventing significantly large particles from being formed or the metal particles which are not granulated from remaining in a large amount. Further, since the moldability is improved, the stability of the shape of the molded body and the like can be particularly enhanced. Further, by setting the content of the binder within the above range, a difference in size between the molded body and the degreased body, that is, so-called a shrinkage ratio is optimized, whereby a decrease in the dimensional accuracy of the finally obtained sintered body can be prevented.

Further, in the granulated powder, any of a variety of additives such as a plasticizer, a lubricant, an antioxidant, a degreasing accelerator, and a surfactant may be added as needed.

Examples of the granulation treatment include a spray drying method, a tumbling granulation method, a fluidized bed granulation method, and a tumbling fluidized bed granulation method.

In the granulation treatment, a solvent which dissolves the binder is used as needed. Examples of the solvent include inorganic solvents such as water and carbon tetrachloride, and organic solvents such as ketone-based solvents, alcohol-based solvents, ether-based solvents, cellosolve-based solvents, aliphatic hydrocarbon-based solvents, aromatic hydrocarbon-based solvents, aromatic heterocyclic compound-based solvents, amide-based solvents, halogen compound-based solvents, ester-based solvents, amine-based solvents, nitrile-based solvents, nitro-based solvents, and aldehyde-based solvents, and one type or a mixture of two or more types selected from these solvents is used.

The average particle diameter of the granulated powder is not particularly limited, but is preferably about 10 μm or more and 200 μm or less, more preferably about 20 μm or more and 100 μm or less, further more preferably about 25 μm or more and 60 μm or less. The granulated powder having such a particle diameter has favorable fluidity, and can more faithfully reflect the shape of a molding die.

The average particle diameter can be obtained as a particle diameter when the cumulative amount obtained by cumulating the percentages of the particles from the smaller diameter side reaches 50% in a cumulative particle size distribution on amass basis obtained by laser diffractometry.

(B) Molding Step

Subsequently, the kneaded material or the granulated powder is molded, whereby a molded body having the same shape as that of a target sintered body is produced.

The method for producing a molded body (molding method) is not particularly limited, and for example, any of a variety of molding methods such as a powder compacting (compression molding) method, a metal injection molding (MIM) method, and an extrusion molding method can be used.

The molding conditions in the case of a powder compacting method among these methods are preferably such that the molding pressure is about 200 MPa or more and 1000 MPa or less (2 t/cm² or more and 10 t/cm² or less), which vary depending on the respective conditions such as the composition and the particle diameter of the metal powder for powder metallurgy to be used, the composition of the binder, and the blending amount thereof.

The molding conditions in the case of a metal injection molding method are preferably such that the material temperature is about 80° C. or higher and 210° C. or lower, and the injection pressure is about 50 MPa or more and 500 MPa or less (0.5 t/cm² or more and 5 t/cm² or less), which vary depending on the respective conditions.

The molding conditions in the case of an extrusion molding method are preferably such that the material temperature is about 80° C. or higher and 210° C. or lower, and the extrusion pressure is about 50 MPa or more and 500 MPa or less (0.5 t/cm² or more and 5 t/cm² or less), which vary depending on the respective conditions.

The thus obtained molded body is in a state where the binder is uniformly distributed in spaces between the particles of the metal powder.

The shape and size of the molded body to be produced are determined in anticipation of shrinkage of the molded body in the subsequent degreasing step and firing step.

(C) Degreasing Step

Subsequently, the thus obtained molded body is subjected to a degreasing treatment (binder removal treatment), whereby a degreased body is obtained.

Specifically, the binder is decomposed by heating the molded body, whereby the binder is removed from the molded body. In this manner, the degreasing treatment is performed.

Examples of the degreasing treatment include a method of heating the molded body and a method of exposing the molded body to a gas capable of decomposing the binder.

In the case of using a method of heating the molded body, the conditions for heating the molded body are preferably such that the temperature is about 100° C. or higher and 750° C. or lower and the time is about 0.1 hours or more and 20 hours or less, and more preferably such that the temperature is about 150° C. or higher and 600° C. or lower and the time is about 0.5 hours or more and 15 hours or less, which slightly vary depending on the composition and the blending amount of the binder. According to this, the degreasing of the molded body can be necessarily and sufficiently performed without sintering the molded body. As a result, it is possible to reliably prevent the binder component from remaining inside the degreased body in a large amount.

The atmosphere when the molded body is heated is not particularly limited, and an atmosphere of a reducing gas such as hydrogen, an atmosphere of an inert gas such as nitrogen or argon, an atmosphere of an oxidative gas such as air, a reduced pressure atmosphere obtained by reducing the pressure of such an atmosphere, or the like can be used.

Examples of the gas capable of decomposing the binder include ozone gas.

Incidentally, by dividing this degreasing step into a plurality of steps in which the degreasing conditions are different, and performing the plurality of steps, the binder in the molded body can be more rapidly decomposed and removed so that the binder does not remain in the molded body.

Further, according to need, the degreased body may be subjected to a machining process such as grinding, polishing, or cutting. The degreased body has a relatively low hardness and relatively high plasticity, and therefore, the machining process can be easily performed while preventing the degreased body from losing its shape. According to such a machining process, a sintered body having high dimensional accuracy can be easily obtained in the end.

(D) Firing Step

The degreased body obtained in the above step (C) is fired in a firing furnace, whereby a sintered body is obtained.

By this firing, in the metal powder for powder metallurgy, diffusion occurs at the boundary surface between the particles, resulting in sintering. At this time, by the mechanism as described above, the degreased body is rapidly sintered. As a result, a sintered body which is dense and has a high density on the whole is obtained.

The firing temperature varies depending on the composition, the particle diameter, and the like of the metal powder for powder metallurgy used in the production of the molded body and the degreased body, but is set to, for example, about 980° C. or higher and 1330° C. or lower, and preferably set to about 1050° C. or higher and 1260° C. or lower.

Further, the firing time is set to 0.2 hours or more and 7 hours or less, but is preferably set to about 1 hour or more and 6 hours or less.

In the firing step, the firing temperature or the below-described firing atmosphere may be changed in the middle of the step.

By setting the firing conditions within such a range, it is possible to sufficiently sinter the entire degreased body while preventing the sintering from proceeding excessively to cause oversintering and increase the size of the crystal structure. As a result, a sintered body having a high density and particularly excellent mechanical properties can be obtained.

Further, since the firing temperature is a relatively low temperature, it is easy to control the heating temperature in the firing furnace to be a fixed temperature, and therefore, it is also easy to maintain the temperature of the degreased body at a fixed temperature. As a result, a more homogeneous sintered body can be produced.

Further, since the firing temperature as described above is a temperature which can be sufficiently realized using a common firing furnace, and therefore, an inexpensive firing furnace can be used, and also the running cost can be kept low. In other words, in the case where the temperature exceeds the above-mentioned firing temperature, it is necessary to employ an expensive firing furnace using a special heat resistant material, and also the running cost may be increased.

The atmosphere when performing firing is not particularly limited, however, in consideration of prevention of significant oxidation of the metal powder, an atmosphere of a reducing gas such as hydrogen, an atmosphere of an inert gas such as argon, a reduced pressure atmosphere obtained by reducing the pressure of such an atmosphere, or the like is preferably used.

The thus obtained sintered body has a high density and excellent mechanical properties. That is, a sintered body produced by molding a composition containing the metal powder for powder metallurgy according to the invention and a binder, followed by degreasing and sintering has a higher relative density than a sintered body obtained by sintering a metal powder in the related art. Therefore, according to the invention, a sintered body having a high density which could not be obtained unless an additional treatment such as an HIP treatment is performed can be realized without performing an additional treatment.

Specifically, according to the invention, for example, the relative density can be expected to be increased by 2% or more as compared with the related art, which slightly varies depending on the composition of the metal powder for powder metallurgy.

As a result, the relative density of the obtained sintered body can be expected to be, for example, 97% or more (preferably 98% or more, more preferably 98.5% or more). The sintered body having a relative density within such a range has excellent mechanical properties comparable to those of ingot materials although it has a shape as close as possible to a desired shape by using a powder metallurgy technique, and therefore, the sintered body can be applied to a variety of machine parts, structural parts, and the like with virtually no post-processing.

Further, the tensile strength and the 0.2% proof stress of a sintered body produced by molding a composition containing the metal powder for powder metallurgy according to the invention and a binder, followed by degreasing and sintering are higher than those of a sintered body obtained by performing sintering in the same manner using a metal powder in the related art. This is considered to be because by optimizing the alloy composition and the particle structure, the sinterability of the metal powder is enhanced, and thus, the mechanical properties of a sintered body to be produced using the metal powder are enhanced.

Further, the sintered body produced as described above has a high surface hardness. Specifically, in the case of, for example, a composition according to austenite stainless steel, the Vickers hardness of the surface of the sintered body is expected to be 140 or more and 500 or less, also preferably expected to be 150 or more and 400 or less, which slightly varies depending on the composition of the metal powder for powder metallurgy. In the case of, for example, a composition according to martensite stainless steel, the Vickers hardness of the surface of the sintered body is expected to be 570 or more and 1200 or less, also preferably expected to be 600 or more and 1000 or less. The sintered body having such a hardness has particularly high durability.

The sintered body has a sufficiently high density and excellent mechanical properties even without performing an additional treatment, however, in order to further increase the density and enhance the mechanical properties, a variety of additional treatments may be performed.

As the additional treatment, for example, an additional treatment of increasing the density such as the HIP treatment described above may be performed, and also a variety of quenching treatments, a variety of sub-zero treatments, a variety of tempering treatments, and the like may be performed. These additional treatments may be performed alone or two or more treatments thereof may be performed in combination.

In the firing step and a variety of additional treatments described above, a light element in the metal powder (in the sintered body) is volatilized, and the composition of the finally obtained sintered body slightly changes from the composition of the metal powder in some cases.

For example, the content of C in the final sintered body may change within the range of 5% or more and 100% or less (preferably within the range of 30% or more and 100% or less) of the content of C in the metal powder for powder metallurgy, which varies depending on the conditions for the step or the conditions for the treatment.

Also the content of 0 in the final sintered body may change within the range of 1% or more and 50% or less (preferably within the range of 3% or more and 50% or less) of the content of 0 in the metal powder for powder metallurgy, which varies depending on the conditions for the step or the conditions for the treatment.

On the other hand, as described above, the produced sintered body may be subjected to an HIP treatment as part of the additional treatments to be performed as needed, however, even if the HIP treatment is performed, a sufficient effect is not exhibited in many cases. In the HIP treatment, the density of the sintered body can be further increased, however, in the first place, the density of the sintered body obtained according to the invention has already been sufficiently increased at the end of the firing step. Therefore, even if the HIP treatment is further performed, densification hardly proceeds any further.

In addition, in the HIP treatment, it is necessary to apply pressure to a material to be treated through a pressure medium, and therefore, the material to be treated may be contaminated, the composition or the physical properties of the material to be treated may unintentionally change accompanying the contamination, or the color of the material to be treated may change accompanying the contamination. Further, by the application of pressure, residual stress is generated or increased in the material to be treated, and a problem such as a change in the shape or a decrease in the dimensional accuracy may occur as the residual stress is released over time.

On the other hand, according to the invention, a sintered body having a sufficiently high density can be produced without performing such an HIP treatment, and therefore, a sintered body having an increased density and also an increased strength can be obtained in the same manner as in the case of performing an HIP treatment. Such a sintered body is less contaminated and discolored, and also an unintended change in the composition or physical properties, or the like occurs less, and also a problem such as a change in the shape or a decrease in the dimensional accuracy occurs less. Therefore, according to the invention, a sintered body having high mechanical strength and dimensional accuracy, and excellent durability can be efficiently produced.

Further, the sintered body produced according to the invention requires almost no additional treatments for enhancing the mechanical properties, and therefore, the composition and the crystal structure tend to become uniform in the entire sintered body. Due to this, the sintered body has high structural anisotropy and therefore has excellent durability against a load from every direction regardless of its shape.

Incidentally, it is confirmed that in the thus produced sintered body, the porosity near the surface thereof is often relatively lower than inside the sintered body. The reason therefor is not clear, however, one of the reasons is that by the addition of the first element and the second element, the sintering reaction more easily proceeds near the surface of the molded body than inside the molded body.

Specifically, when the porosity near the surface of the sintered body is represented by A1 and the porosity inside the sintered body is represented by A2, A2−A1 is preferably 0.1% or more and 3% or less, more preferably 0.2% or more and 2% or less. The sintered body showing the value of A2−A1 within the above range not only has necessary and sufficient mechanical strength, but also can easily flatten the surface. That is, by polishing the surface of such a sintered body, a surface having high specularity can be obtained.

Such a sintered body having high specularity not only has high mechanical strength, but also has excellent aesthetic properties. Therefore, such a sintered body is favorably used also for application requiring excellent aesthetic appearance.

Incidentally, the porosity A1 near the surface of the sintered body refers to a porosity in a 25-μm radius region centered on the position at a depth of 50 μm from the surface of the cross section of the sintered body. Further, the porosity A2 inside the sintered body refers to a porosity in a 25-μm radius region centered on the position at a depth of 300 μm from the surface of the cross section of the sintered body. These porosities are values obtained by observing the cross section of the sintered body with a scanning electron microscope and dividing the area of pores present in the region by the area of the region.

Hereinabove, the metal powder for powder metallurgy, the compound, the granulated powder, and the sintered body according to the invention have been described with reference to preferred embodiments, however, the invention is not limited thereto.

Further, the sintered body according to the invention is used for, for example, parts for transport machinery such as parts for automobiles, parts for bicycles, parts for railroad cars, parts for ships, parts for airplanes, and parts for space transport machinery (such as rockets); parts for electronic devices such as parts for personal computers and parts for mobile phone terminals; parts for electrical devices such as refrigerators, washing machines, and cooling and heating machines; parts for machines such as machine tools and semiconductor production devices; parts for plants such as atomic power plants, thermal power plants, hydroelectric power plants, oil refinery plants, and chemical complexes; parts for timepieces, metallic tableware, jewels, ornaments such as frames for glasses, and all other sorts of structural parts.

EXAMPLES

Next, Examples of the invention will be described.

1. Production of Sintered Body (Zr—Nb Based) Sample No. 1

(1) First, a metal powder having a composition shown in Table 1 produced by a water atomization method was prepared. This metal powder had an average particle diameter of 4.05 μm, a tap density of 4.15 g/cm³, and a specific surface area of 0.21 m²/g.

The composition of the powder shown in Table 1 was identified and quantitatively determined by an inductively coupled high-frequency plasma optical emission spectrometry (ICP analysis method). In the ICP analysis, an ICP device (model: CIROS-120) manufactured by Rigaku Corporation was used. Further, in the identification and determination of C, a carbon-sulfur analyzer (CS-200) manufactured by LECO Corporation was used. Further, in the identification and determination of 0, an oxygen-nitrogen analyzer (TC-300/EF-300) manufactured by LECO Corporation was used.

(2) Subsequently, the metal powder and a mixture (organic binder) of polypropylene and a wax were weighed at a mass ratio of 9:1 and mixed with each other, whereby a mixed starting material was obtained.

(3) Subsequently, this mixed starting material was kneaded using a kneader, whereby a compound was obtained.

(4) Subsequently, this compound was molded using an injection molding device under the following molding conditions, whereby a molded body was produced.

Molding Conditions

-   -   Material temperature: 150° C.     -   Injection pressure: 11 MPa (110 kgf/cm²)

(5) Subsequently, the obtained molded body was subjected to a heat treatment (degreasing treatment) under the following degreasing conditions, whereby a degreased body was obtained.

Degreasing Conditions

-   -   Degreasing temperature: 500° C.     -   Degreasing time: 1 hour (retention time at the degreasing         temperature)     -   Degreasing atmosphere: nitrogen atmosphere

(6) Subsequently, the obtained degreased body was fired under the following firing conditions, whereby a sintered body was obtained. The shape of the sintered body was determined to be a cylinder with a diameter of 10 mm and a thickness of 5 mm.

Firing Conditions

-   -   Firing temperature: 1200° C.     -   Firing time: 3 hours (retention time at the firing temperature)     -   Firing atmosphere: argon atmosphere

Sample Nos. 2 to 30

Sintered bodies were obtained in the same manner as the method for producing the sintered body of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 1, respectively. The sintered body of sample No. 30 was obtained by performing an HIP treatment under the following conditions after firing. Further, the sintered bodies of sample Nos. 18 to 20 were obtained by using the metal powder produced by a gas atomization method, respectively, and indicated by “gas” in the column of Remarks in Table 1.

HIP Treatment Conditions

-   -   Heating temperature: 1100° C.     -   Heating time: 2 hours     -   Applied pressure: 100 MPa

TABLE 1 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 1 Example 16.43 12.48 0.73 0.018 0.09 0.07 2.11 0.06 0.28 remainder 1.29 0.16 0.22 8.89 No. 2 Example 17.12 12.63 0.58 0.023 0.07 0.05 2.43 0.12 0.31 remainder 1.40 0.12 0.21 5.22 No. 3 Example 17.87 13.24 0.65 0.029 0.05 0.09 2.04 0.07 0.42 remainder 0.56 0.14 0.22 4.83 No. 4 Example 16.19 14.71 0.84 0.011 0.05 0.05 2.89 0.08 0.25 remainder 1.00 0.10 0.12 9.09 No. 5 Example 17.55 13.88 0.75 0.026 0.09 0.10 2.61 0.11 0.36 remainder 0.90 0.19 0.25 7.31 No. 6 Example 16.79 11.58 0.52 0.068 0.12 0.03 2.74 0.12 0.22 remainder 4.00 0.15 0.29 2.21 No. 7 Example 17.49 13.21 0.69 0.054 0.03 0.12 2.15 0.79 0.41 remainder 0.25 0.15 0.22 2.78 No. 8 Example 16.88 14.15 0.77 0.024 0.24 0.09 2.23 0.28 0.48 remainder 2.67 0.33 0.43 13.75 No. 9 Example 17.32 12.65 0.48 0.021 0.08 0.26 2.81 0.17 0.29 remainder 0.31 0.34 0.71 16.19 No. 10 Example 17.25 12.87 0.35 0.065 0.09 0.05 2.15 0.35 0.62 remainder 1.80 0.14 0.40 2.15 No. 11 Example 17.66 12.55 0.96 0.017 0.07 0.07 2.24 0.05 0.25 remainder 1.00 0.14 0.15 8.24 No. 12 Example 16.87 12.91 1.12 0.025 0.15 0.19 2.13 0.05 0.25 remainder 0.79 0.34 0.30 13.60 No. 13 Example 16.78 12.19 0.54 0.019 0.36 0.42 2.25 0.07 0.58 remainder 0.86 0.78 1.44 41.05 No. 14 Example 16.77 12.89 0.91 0.024 0.14 0.17 2.13 0.05 0.25 remainder 0.82 0.31 0.34 12.92 No. 15 Example 16.47 12.57 0.87 0.023 0.13 0.15 2.04 0.05 0.25 remainder 0.87 0.28 0.32 12.17 No. 16 Example 16.75 12.58 0.68 0.007 0.05 0.09 2.84 0.12 0.28 remainder 0.56 0.14 0.21 20.00 No. 17 Example 17.22 13.54 0.84 0.152 0.08 0.05 2.84 0.12 0.28 remainder 1.60 0.13 0.15 0.86 No. 18 Example 16.45 12.55 0.72 0.023 0.08 0.08 1.95 0.08 0.07 remainder 1.00 0.16 0.22 6.96 gas No. 19 Example 17.26 12.57 0.59 0.032 0.07 0.06 2.64 0.02 0.08 remainder 1.17 0.13 0.22 4.06 gas No. 20 Example 17.64 13.41 0.63 0.015 0.04 0.07 2.04 0.06 0.10 remainder 0.57 0.11 0.17 7.33 gas No. 21 Compar- 16.34 12.84 0.75 0.025 0.00 0.07 2.36 0.11 0.29 remainder 0.00 0.07 0.09 2.80 ative Example No. 22 Compar- 17.22 13.32 0.79 0.032 0.05 0.00 2.28 0.09 0.31 remainder — 0.05 0.06 1.56 ative Example No. 23 Compar- 16.75 14.23 0.75 0.015 0.00 0.00 2.33 0.12 0.33 remainder — 0.00 0.00 0.00 ative Example No. 24 Compar- 16.43 12.45 0.88 0.021 0.68 0.07 2.58 0.11 0.38 remainder 9.71 0.75 0.85 35.71 ative Example No. 25 Compar- 16.35 13.04 0.66 0.035 0.06 0.71 2.36 0.05 0.41 remainder 0.08 0.77 1.17 22.00 ative Example No. 26 Compar- 17.56 13.25 0.15 0.011 0.06 0.07 2.77 0.11 0.27 remainder 0.86 0.13 0.87 11.82 ative Example No. 27 Compar- 17.63 13.54 0.95 0.061 0.04 0.08 2.89 0.32 0.45 remainder 0.50 0.12 0.06 1.97 ative Example No. 28 Compar- 17.56 13.25 0.66 0.002 0.01 0.01 2.77 0.11 0.27 remainder 1.00 0.02 0.03 10.00 ative Example No. 29 Compar- 17.56 13.25 0.35 0.380 0.22 0.07 2.68 0.24 0.45 remainder 3.14 0.29 0.83 0.76 ative Example No. 30 Compar- 17.34 12.84 0.75 0.025 0.00 0.07 2.36 0.11 0.29 remainder — 0.07 0.09 2.80 HIP ative treatment Example

In Table 1, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Table 1 is omitted.

Sample Nos. 31 to 48

Sintered bodies were obtained in the same manner as the method for producing the sintered body of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 2, respectively. The sintered body of sample No. 48 was obtained by performing an HIP treatment under the following conditions after firing. Further, the sintered bodies of sample Nos. 41 to 43 were obtained by using the metal powder produced by a gas atomization method, respectively, and indicated by “gas” in the column of Remarks in Table 2.

HIP Treatment Conditions

-   -   Heating temperature: 1100° C.     -   Heating time: 2 hours     -   Applied pressure: 100 MPa

TABLE 2 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 31 Example 18.94 13.59 0.77 0.048 0.11 0.09 3.48 0.08 0.48 remainder 1.22 0.20 0.26 4.17 No. 32 Example 18.15 14.75 0.51 0.021 0.08 0.08 3.08 0.95 0.42 remainder 1.00 0.16 0.31 7.62 No. 33 Example 19.63 11.39 0.32 0.074 0.09 0.05 3.92 0.35 0.62 remainder 1.80 0.14 0.44 1.89 No. 34 Example 18.67 13.44 0.98 0.065 0.18 0.04 3.32 0.07 0.28 remainder 4.50 0.22 0.22 3.38 No. 35 Example 18.03 14.87 0.51 0.005 0.04 0.08 3.15 0.02 0.35 remainder 0.50 0.12 0.24 24.00 No. 36 Example 19.78 12.35 0.42 0.178 0.09 0.08 3.87 0.35 0.62 remainder 1.13 0.17 0.40 0.96 No. 37 Example 18.65 13.42 0.87 0.061 0.17 0.04 3.29 0.07 0.28 remainder 4.25 0.21 0.24 3.44 No. 38 Example 18.63 13.46 0.94 0.063 0.16 0.05 3.27 0.07 0.28 remainder 3.20 0.21 0.22 3.33 No. 39 Example 22.54 13.59 0.86 0.066 0.08 0.08 0.00 0.09 0.26 remainder 1.00 0.16 0.19 2.42 No. 40 Example 25.41 21.36 1.16 0.053 0.06 0.08 0.00 0.07 0.27 remainder 0.75 0.14 0.12 2.64 No. 41 Example 18.88 13.54 0.87 0.056 0.12 0.11 3.52 0.11 0.12 remainder 1.09 0.23 0.26 4.11 gas No. 42 Example 18.21 14.81 0.48 0.025 0.07 0.09 3.11 0.98 0.11 remainder 0.78 0.16 0.33 6.40 gas No. 43 Example 19.57 11.44 0.31 0.068 0.08 0.06 4.02 0.51 0.16 remainder 1.33 0.14 0.45 2.06 gas No. 44 Compar- 18.87 11.24 0.57 0.056 0.00 0.07 3.47 0.22 0.29 remainder 0.00 0.07 0.12 1.25 ative Example No. 45 Compar- 19.56 14.15 0.79 0.032 0.15 0.00 3.75 0.09 0.31 remainder — 0.15 0.19 4.69 ative Example No. 46 Compar- 18.78 11.42 0.88 0.012 0.58 0.07 2.58 0.11 0.38 remainder 8.29 0.65 0.74 54.17 ative Example No. 47 Compar- 19.65 14.51 0.66 0.053 0.06 0.89 2.36 0.05 0.41 remainder 0.07 0.95 1.44 17.92 ative Example No. 48 Compar- 18.87 11.24 0.57 0.056 0.00 0.07 3.47 0.22 0.29 remainder 0.00 0.07 0.12 1.25 HIP ative treatment Example

In Table 2, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Table 2 is omitted.

Sample Nos. 49 to 66

Sintered bodies were obtained in the same manner as the method for producing the sintered body of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 3, respectively. The sintered body of sample No. 66 was obtained by performing an HIP treatment under the following conditions after firing. Further, the sintered bodies of sample Nos. 59 to 61 were obtained by using the metal powder produced by a gas atomization method, respectively, and indicated by “gas” in the column of Remarks in Table 3.

HIP Treatment Conditions

-   -   Heating temperature: 1100° C.     -   Heating time: 2 hours     -   Applied pressure: 100 MPa

TABLE 3 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 49 Example 19.21 8.34 0.62 0.038 0.08 0.06 0.00 0.21 0.48 remainder 1.33 0.14 0.23 3.68 No. 50 Example 19.74 9.56 0.88 0.041 0.05 0.10 0.08 0.04 0.55 remainder 0.50 0.15 0.17 3.66 No. 51 Example 18.30 10.12 0.44 0.019 0.15 0.09 0.05 0.07 0.68 remainder 1.67 0.24 0.55 12.63 No. 52 Example 19.35 8.19 1.05 0.069 0.08 0.06 0.00 0.05 0.18 remainder 1.33 0.14 0.13 2.03 No. 53 Example 19.45 9.65 0.88 0.007 0.05 0.10 0.08 0.00 0.55 remainder 0.50 0.15 0.17 21.43 No. 54 Example 18.25 10.25 0.44 0.256 0.15 0.09 0.05 0.07 0.68 remainder 1.67 0.24 0.55 0.94 No. 55 Example 20.58 21.54 1.15 0.074 0.05 0.09 0.00 1.23 0.75 remainder 0.56 0.14 0.12 1.89 No. 56 Example 20.34 19.25 1.02 0.068 0.05 0.09 0.00 1.23 0.75 remainder 0.56 0.14 0.14 2.06 No. 57 Example 16.58 7.45 0.56 0.128 0.06 0.08 0.05 0.48 0.25 remainder 0.75 0.14 0.25 1.09 No. 58 Example 15.72 10.25 0.36 0.058 0.04 0.09 2.54 0.07 0.21 remainder 0.44 0.13 0.36 2.24 No. 59 Example 19.11 8.43 0.64 0.045 0.07 0.07 0.00 0.23 0.12 remainder 1.00 0.14 0.22 3.11 gas No. 60 Example 19.72 9.65 0.85 0.048 0.06 0.11 0.09 0.05 0.14 remainder 0.55 0.17 0.20 3.54 gas No. 61 Example 18.25 10.21 0.46 0.015 0.12 0.12 0.06 0.09 0.18 remainder 1.00 0.24 0.52 16.00 gas No. 62 Compar- 19.11 8.48 0.74 0.064 0.00 0.05 0.00 0.18 0.28 remainder 0.00 0.05 0.07 0.78 ative Example No. 63 Compar- 18.78 9.77 0.79 0.023 0.08 0.00 0.02 0.09 0.31 remainder — 0.08 0.10 3.48 ative Example No. 64 Compar- 18.42 8.21 0.39 0.012 0.69 0.07 0.03 0.11 0.38 remainder 9.86 0.76 1.95 62.33 ative Example No. 65 Compar- 19.21 8.55 0.42 0.021 0.06 0.61 0.02 0.15 0.32 remainder 0.10 0.67 1.60 31.90 ative Example No. 66 Compar- 19.11 8.48 0.74 0.064 0.00 0.05 0.00 0.18 0.28 remainder 0.00 0.05 0.07 0.78 HIP ative treatment Example

In Table 3, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Table 3 is omitted.

Sample No. 67

(1) First, a metal powder having a composition shown in Table 4 was produced by a water atomization method in the same manner as in the case of sample No. 1.

(2) Subsequently, the metal powder was granulated by a spray drying method. The binder used at this time was polyvinyl alcohol, which was used in an amount of 1 part by mass with respect to 100 parts by mass of the metal powder. Further, a solvent (ion exchanged water) was used in an amount of 50 parts by mass with respect to 1 part by mass of polyvinyl alcohol. In this manner, a granulated powder having an average particle diameter of 50 μm was obtained.

(3) Subsequently, this granulated powder was subjected to powder compacting under the following molding conditions. In this molding, a press molding machine was used. The shape of the molded body to be produced was determined to be a cube with a side length of 20 mm.

Molding Conditions

-   -   Material temperature: 90° C.     -   Molding pressure: 600 MPa (6 t/cm²)

(4) Subsequently, the obtained molded body was subjected to a heat treatment (degreasing treatment) under the following degreasing conditions, whereby a degreased body was obtained.

Degreasing Conditions

-   -   Degreasing temperature: 450° C.     -   Degreasing time: 2 hours (retention time at the degreasing         temperature)     -   Degreasing atmosphere: nitrogen atmosphere

(5) Subsequently, the obtained degreased body was fired under the following firing conditions, whereby a sintered body was obtained.

Firing Conditions

-   -   Firing temperature: 1200° C.     -   Firing time: 3 hours (retention time at the firing temperature)     -   Firing atmosphere: argon atmosphere

Sample Nos. 68 to 85

Sintered bodies were obtained in the same manner as in the case of sample No. 67 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 4, respectively. The sintered body of sample No. 85 was obtained by performing an HIP treatment under the following conditions after firing.

HIP Treatment Conditions

-   -   Heating temperature: 1100° C.     -   Heating time: 2 hours     -   Applied pressure: 100 MPa

TABLE 4 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 67 Example 16.43 12.48 0.73 0.018 0.09 0.07 2.11 0.06 0.28 remainder 1.29 0.16 0.22 8.89 Powder compacting No. 68 Example 17.12 12.63 0.58 0.023 0.07 0.05 2.43 0.12 0.31 remainder 1.40 0.12 0.21 5.22 Powder compacting No. 69 Example 17.87 13.24 0.65 0.029 0.05 0.09 2.04 0.07 0.42 remainder 0.56 0.14 0.22 4.83 Powder compacting No. 70 Example 16.19 14.71 0.84 0.011 0.05 0.05 2.89 0.08 0.25 remainder 1.00 0.10 0.12 9.09 Powder compacting No. 71 Example 17.55 13.88 0.75 0.026 0.09 0.10 2.61 0.11 0.36 remainder 0.90 0.19 0.25 7.31 Powder compacting No. 72 Example 16.79 11.58 0.52 0.068 0.12 0.03 2.74 0.12 0.22 remainder 4.00 0.15 0.29 2.21 Powder compacting No. 73 Example 17.49 13.21 0.69 0.054 0.03 0.12 2.15 0.79 0.41 remainder 0.25 0.15 0.22 2.78 Powder compacting No. 74 Example 16.88 14.15 0.77 0.024 0.24 0.09 2.23 0.28 0.48 remainder 2.67 0.33 0.43 13.75 Powder compacting No. 75 Example 17.32 12.65 0.48 0.021 0.08 0.26 2.81 0.17 0.29 remainder 0.31 0.34 0.71 16.19 Powder compacting No. 76 Example 17.25 12.87 0.35 0.065 0.09 0.05 2.15 0.35 0.62 remainder 1.80 0.14 0.40 2.15 Powder compacting No. 77 Example 17.66 12.55 0.96 0.017 0.07 0.07 2.24 0.05 0.25 remainder 1.00 0.14 0.15 8.24 Powder compacting No. 78 Example 16.87 12.91 1.12 0.025 0.15 0.19 2.13 0.05 0.25 remainder 0.79 0.34 0.30 13.60 Powder compacting No. 79 Example 16.78 12.19 0.54 0.019 0.36 0.42 2.25 0.07 0.58 remainder 0.86 0.78 1.44 41.05 Powder compacting No. 80 Compar- 16.34 12.84 0.75 0.025 0.00 0.07 2.36 0.11 0.29 remainder 0.00 0.07 0.09 2.80 Powder ative compacting Example No. 81 Compar- 17.22 13.32 0.79 0.032 0.05 0.00 2.28 0.09 0.31 remainder — 0.05 0.06 1.56 Powder ative compacting Example No. 82 Compar- 16.75 14.23 0.75 0.015 0.00 0.00 2.33 0.12 0.33 remainder — 0.00 0.00 0.00 Powder ative compacting Example No. 83 Compar- 16.43 12.45 0.88 0.021 0.68 0.07 2.58 0.11 0.38 remainder 9.71 0.75 0.85 35.71 Powder ative compacting Example No. 84 Compar- 16.35 13.04 0.66 0.035 0.06 0.71 2.36 0.05 0.41 remainder 0.08 0.77 1.17 22.00 Powder ative compacting Example No. 85 Compar- 16.34 12.84 0.75 0.025 0.00 0.07 2.36 0.11 0.29 remainder — 0.07 0.09 2.80 HIP ative treatment Example

In Table 4, among the metal powders for powder metallurgy and the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Table 4 is omitted.

Sample Nos. 86 to 101

Sintered bodies were obtained in the same manner as in the case of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 5, respectively.

TABLE 5 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 86 Example 3.98 0.08 0.69 1.437 0.07 0.07 4.97 0.00 0.19 remainder 1.00 0.14 0.20 0.10 W; 6.10 Co: 8.46 No. 87 Example 4.11 0.11 0.74 1.423 0.11 0.04 4.88 0.00 0.28 remainder 2.75 0.15 0.20 0.11 W: 5.86 Co: 8.31 No. 88 Example 4.03 0.05 0.63 1.479 0.05 0.12 5.09 0.00 0.25 remainder 0.42 0.17 0.27 0.11 W: 6.31 Co: 8.07 No. 89 Compar- 4.11 0.06 0.79 1.426 0.05 0.00 5.11 0.00 0.23 remainder — 0.05 0.06 0.04 W: 6.08 ative Co: 8.58 Example No. 90 Example 1.06 0.02 0.73 0.724 0.08 0.08 0.19 0.78 0.25 remainder 1.00 0.16 0.22 0.22 No. 91 Example 0.98 0.02 0.74 0.698 0.11 0.04 0.16 0.81 0.26 remainder 2.75 0.15 0.20 0.21 No. 92 Example 1.04 0.03 0.82 0.711 0.05 0.12 0.21 0.63 0.24 remainder 0.42 0.17 0.21 0.24 Al: 0.02 No. 93 Compar- 0.99 0.19 0.79 0.711 0.16 0.00 0.27 0.88 0.35 remainder — 0.16 0.20 0.23 Al: 0.06 ative Example No. 94 Example 12.88 0.07 0.73 0.900 0.07 0.07 0.00 0.10 0.27 remainder 1.00 0.14 0.19 0.16 No. 95 Example 13.37 0.10 0.64 0.850 0.10 0.05 0.00 0.08 0.25 remainder 2.00 0.51 0.23 0.18 No. 96 Example 12.54 0.06 0.75 0.980 0.05 0.10 0.00 0.11 0.29 remainder 0.50 0.15 0.20 0.15 No. 97 Compar- 12.95 0.10 0.78 0.760 0.04 0.00 0.00 0.08 0.31 remainder — 0.04 0.05 0.05 ative Example No. 98 Example 16.43 4.12 0.73 0.018 0.09 0.32 0.00 0.00 0.28 remainder 0.28 0.41 0.56 22.78 Cu: 3.98 No. 99 Example 16.19 3.89 0.36 0.052 0.05 0.29 0.00 0.00 0.25 remainder 0.17 0.34 0.94 6.54 Cu: 4.56 No. 100 Example 16.88 4.05 1.63 0.069 0.12 0.18 0.00 0.00 0.36 remainder 0.67 0.30 0.18 4.35 Cu: 4.78 No. 101 Compar- 17.18 3.54 0.62 0.024 0.05 0.00 0.00 0.00 0.32 remainder — 0.05 0.28 2.08 Cu: 4.31 ative Example

In Table 5, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Table 5 is omitted.

2. Evaluation of Metal Powder (Zr—Nb Based)

With respect to the particle of the metal powder for powder metallurgy of sample No. 1 corresponding to Example, an analysis in the depth direction by Auger electron spectroscopy in combination with sputtering was performed.

Then, the time of execution of sputtering was converted into a depth from the surface of the particle (sputter depth) and shown on the horizontal axis, and also the content of an atom (atomic concentration) determined by the Auger electron spectroscopy was shown on the vertical axis, and the analytical results were plotted, whereby Auger electron spectra were obtained.

The Auger electron spectra obtained from the particle of the metal powder for powder metallurgy of sample No. 1 are shown in FIG. 3. The four horizontal straight lines drawn overlapping the spectra indicate the contents of Fe, Cr, Si, and O in the whole particle of sample No. 1, respectively.

As apparent from FIG. 3, in the particle of sample No. 1, the content of Cr little fluctuates in a region from the surface (at a depth of 0 nm) to a depth of 60 nm. Accordingly, it is confirmed that the content of Cr on the surface of the particle (Cr(0)) falls within the range of 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)).

Further, it is also confirmed that the content of Cr on the surface of the particle (Cr(0)) falls within the range of 0.2% by atom or more and 15% by atom or less.

On the other hand, also with respect to the particle of the metal powder for powder metallurgy of sample No. 23 corresponding to Comparative Example, an analysis in the depth direction by Auger electron spectroscopy in combination with sputtering was performed in the same manner.

The Auger electron spectra obtained from the particle of the metal powder for powder metallurgy of sample No. 23 are shown in FIG. 4. The four horizontal straight lines drawn overlapping the spectra indicate the contents of Fe, Cr, Si, and O in the whole particle of sample No. 23, respectively.

As apparent from FIG. 4, it is confirmed that in the particle of sample No. 23, the content of Cr relatively largely fluctuates in a region from the surface to a depth of 60 nm.

Further, it is confirmed that the content of Cr on the surface of the particle (Cr(0)) exceeds 15% by atom.

Incidentally, also with respect to the particles of sample Nos. other than sample No. 1 and sample No. 23, the content of Cr was determined in the same manner.

The determined contents are shown in Tables 6 and 10.

Further, with respect to the particles of the respective sample Nos., the content of Si on the surface of the particle (Si(0)), the content of Si at a depth of 60 nm from the surface of the particle (Si(60)), and the content of O on the surface of the particle (O(0)) were determined.

The determined contents are shown in Tables 6 and 10.

3. Evaluation of Sintered Body (Zr—Nb Based) 3.1 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Tables 1 to 5, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Tables 6 to 10.

3.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Tables 1 to 4, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Tables 6 to 9.

3.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Tables 1 to 4, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of these physical properties were evaluated according to the following evaluation criteria.

Evaluation Criteria for Tensile Strength (Tables 6 and 9)

A: The tensile strength of the sintered body is 520 MPa or more.

B: The tensile strength of the sintered body is 510 MPa or more and less than 520 MPa.

C: The tensile strength of the sintered body is 500 MPa or more and less than 510 MPa.

D: The tensile strength of the sintered body is 490 MPa or more and less than 500 MPa.

E: The tensile strength of the sintered body is 480 MPa or more and less than 490 MPa.

F: The tensile strength of the sintered body is less than 480 MPa.

Evaluation Criteria for Tensile Strength (Tables 7 and 8)

A: The tensile strength of the sintered body is 560 MPa or more.

B: The tensile strength of the sintered body is 550 MPa or more and less than 560 MPa.

C: The tensile strength of the sintered body is 540 MPa or more and less than 550 MPa.

D: The tensile strength of the sintered body is 530 MPa or more and less than 540 MPa.

E: The tensile strength of the sintered body is 520 MPa or more and less than 530 MPa.

F: The tensile strength of the sintered body is less than 520 MPa.

Evaluation Criteria for 0.2% Proof Stress (Tables 6 and 9)

A: The 0.2% proof stress of the sintered body is 195 MPa or more.

B: The 0.2% proof stress of the sintered body is 190 MPa or more and less than 195 MPa.

C: The 0.2% proof stress of the sintered body is 185 MPa or more and less than 190 MPa.

D: The 0.2% proof stress of the sintered body is 180 MPa or more and less than 185 MPa.

E: The 0.2% proof stress of the sintered body is 175 MPa or more and less than 180 MPa.

F: The 0.2% proof stress of the sintered body is less than 175 MPa.

Evaluation Criteria for 0.2% Proof Stress (Tables 7 and 8)

A: The 0.2% proof stress of the sintered body is 225 MPa or more.

B: The 0.2% proof stress of the sintered body is 220 MPa or more and less than 225 MPa.

C: The 0.2% proof stress of the sintered body is 215 MPa or more and less than 220 MPa.

D: The 0.2% proof stress of the sintered body is 210 MPa or more and less than 215 MPa.

E: The 0.2% proof stress of the sintered body is 205 MPa or more and less than 210 MPa.

F: The 0.2% proof stress of the sintered body is less than 205 MPa.

Evaluation Criteria for Elongation

A: The elongation of the sintered body is 48% or more.

B: The elongation of the sintered body is 46% or more and less than 48%.

C: The elongation of the sintered body is 44% or more and less than 46%.

D: The elongation of the sintered body is 42% or more and less than 44%.

E: The elongation of the sintered body is 40% or more and less than 42%.

F: The elongation of the sintered body is less than 40%.

The above evaluation results are shown in Tables 6 to 9. As described above, the evaluation criteria are different between Tables 6 and 9 and Tables 7 and 8 depending on the values of the physical properties.

3.4 Evaluation of Fatigue Strength

With respect to the sintered bodies of the respective sample Nos. shown in Tables 1 to 4, the fatigue strength was measured.

The fatigue strength was measured in accordance with the test method specified in JIS Z 2273 (1978). The waveform of an applied load corresponding to a repeated stress was set to an alternating sine wave, and the minimum/maximum stress ratio (minimum stress/maximum stress) was set to 0.1. Further, the repeated frequency was set to 30 Hz, and the repeat count was set to 1×10⁷.

Then, the measured fatigue strength was evaluated according to the following evaluation criteria.

Evaluation Criteria for Fatigue Strength

A: The fatigue strength of the sintered body is 260 MPa or more.

B: The fatigue strength of the sintered body is 240 MPa or more and less than 260 MPa.

C: The fatigue strength of the sintered body is 220 MPa or more and less than 240 MPa.

D: The fatigue strength of the sintered body is 200 MPa or more and less than 220 MPa.

E: The fatigue strength of the sintered body is 180 MPa or more and less than 200 MPa.

F: The fatigue strength of the sintered body is less than 180 MPa.

The above evaluation results are shown in Tables 6 to 9.

TABLE 6 Metal powder Average particle Cr(0)/ Si(0)/ O(0)/ Sample diameter Cr(0) Cr(60) Cr(60) Si(0) Si(60) Si(60) O(0) Si(0) No. — μm at % at % % at % at % % at % — No. 1 Example 4.05  9.9 7.2 137.5 36.5 18.3 199.5  8.2 0.22 No. 2 Example 3.79  6.7 8.5  78.8 41.3 16.8 245.8  9.8 0.24 No. 3 Example 3.84 12.4 7.7 161.0 28.6  6.7 426.9  7.2 0.25 No. 4 Example 3.92 — — — — — — — — No. 5 Example 4.56 — — — — — — — — No. 6 Example 3.68 — — — — — — — — No. 7 Example 3.77 — — — — — — — — No. 8 Example 3.81 — — — — — — — — No. 9 Example 3.85 — — — — — — — — No. 10 Example 4.23 — — — — — — — — No. 11 Example 3.21 — — — — — — — — No. 12 Example 3.36 — — — — — — — — No. 13 Example 6.18 — — — — — — — — No. 14 Example 10.8 — — — — — — — — No. 15 Example 15.4 — — — — — — — — No. 16 Example 5.23 — — — — — — — — No. 17 Example 4.42 — — — — — — — — No. 18 Example 8.11 — — — — — — — — No. 19 Example 7.65 — — — — — — — — No. 20 Example 7.25 — — — — — — — — No. 21 Compar- 3.77 20.4 9.5 214.7 22.6 15.2 148.7 10.1 0.45 ative Example No. 22 Compar- 3.94 19.3 10.1  191.1 19.8 12.4 159.7 12.8 0.65 ative Example No. 23 Compar- 3.65 18.5 10.8  171.3 24.8 16.5 150.3 11.0 0.44 ative Example No. 24 Compar- 4.87 — — — — — — — — ative Example No. 25 Compar- 4.25 — — — — — — — — ative Example No. 26 Compar- 3.64 — — — — — — — — ative Example No. 27 Compar- 3.55 — — — — — — — — ative Example No. 28 Compar- 4.87 — — — — — — — — ative Example No. 29 Compar- 4.66 — — — — — — — — ative Example No. 30 Compar- 3.77 — — — — — — — — ative Example Evaluation results of sintered body 0.2% Relative Vickers Tensile proof Elonga- Fatigue Sample density hardness strength stress tion strength No. — % — — — — — No. 1 Example 99.5 165 A A A A No. 2 Example 99.6 175 A A A A No. 3 Example 99.3 171 A A A A No. 4 Example 98.8 153 B A A A No. 5 Example 99.7 182 A A A A No. 6 Example 98.7 154 B B A B No. 7 Example 98.8 156 B B A B No. 8 Example 98.3 149 B B A B No. 9 Example 98.1 148 B B B B No. 10 Example 98.5 152 B B A B No. 11 Example 98.1 146 B B B B No. 12 Example 97.8 144 B B C B No. 13 Example 97.6 142 C C C C No. 14 Example 97.5 144 B C C C No. 15 Example 97.2 141 C C C C No. 16 Example 97.8 141 B B B B No. 17 Example 97.3 163 B B C B No. 18 Example 99.3 161 A A A A No. 19 Example 99.4 171 A A A A No. 20 Example 99.1 164 A A A A No. 21 Compar- 96.4 128 D D B D ative Example No. 22 Compar- 96.8 134 D D B D ative Example No. 23 Compar- 96.2 123 E E C E ative Example No. 24 Compar- 94.7 115 D D D D ative Example No. 25 Compar- 94.6 118 D D E D ative Example No. 26 Compar- 94.5 102 E E C E ative Example No. 27 Compar- 92.6 135 F F E F ative Example No. 28 Compar- 95.3 118 D D B D ative Example No. 29 Compar- 93.2 138 E E F E ative Example No. 30 Compar- 99.2 175 A A B A ative Example

TABLE 7 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Fatigue Sample diameter density hardness strength stress tion strength No. — μm % — — — — — No. 31 Example 5.68 99.3 178 A A A A No. 32 Example 4.79 99.5 185 A A A A No. 33 Example 4.05 98.6 167 B B A B No. 34 Example 3.81 98.8 158 B B A B No. 35 Example 3.05 98.2 162 B B B B No. 36 Example 4.25 97.6 154 B B C B No. 37 Example 9.86 97.8 158 B B B B No. 38 Example 14.2 97.5 154 B C C C No. 39 Example 2.56 98.6 171 B B A A No. 40 Example 14.2 98.3 173 B B A A No. 41 Example 11.53 99.1 174 A A A A No. 42 Example 9.64 99.2 180 A A A A No. 43 Example 8.25 98.3 163 B B A B No. 44 Compar- 5.32 96.4 127 D D B D ative Example No. 45 Compar- 5.48 96.7 136 D D B D ative Example No. 46 Compar- 4.23 95.2 121 D D D D ative Example No. 47 Compar- 4.51 94.8 105 E E F E ative Example No. 48 Compar- 5.32 99.2 174 A A B A ative Example

TABLE 8 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Fatigue Sample diameter density hardness strength stress tion strength No. — μm % — — — — — No. 49 Example 3.97 99.6 172 A A A A No. 50 Example 3.25 99.3 167 A A B A No. 51 Example 6.54 98.4 142 A A B A No. 52 Example 5.48 98.2 157 B B B B No. 53 Example 3.92 98.4 161 B B B B No. 54 Example 3.74 97.3 148 B B C B No. 55 Example 16.45 97.1 137 C C C C No. 56 Example 22.1 97.0 135 c C C C No. 57 Example 10.05 97.5 138 B B B B No. 58 Example 7.23 98.8 165 B B A B No. 59 Example 8.12 99.3 165 A A A A No. 60 Example 7.22 99.0 160 A A B A No. 61 Example 13.65 98.2 134 A A B A No. 62 Compar- 3.89 96.3 127 D D B D ative Example No. 63 Compar- 3.47 96.7 136 D D B D ative Example No. 64 Compar- 4.25 94.7 116 D D D D ative Example No. 65 Compar- 3.64 95.2 119 D D E D ative Example No. 66 Compar- 3.89 99.4 170 A A B A ative Example

TABLE 9 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Fatigue Sample diameter density hardness strength stress tion strength No. — μm % — — — — — No. 67 Example 4.05 99.6 168 A A A A No. 68 Example 3.79 99.6 177 A A A A No. 69 Example 3.84 99.4 172 A A A A No. 70 Example 3.92 98.9 155 B A A A No. 71 Example 4.56 99.7 183 A A A A No. 72 Example 3.68 98.9 158 B B A B No. 73 Example 3.77 99.0 162 B B A B No. 74 Example 3.81 98.5 155 B B A B No. 75 Example 3.85 98.4 156 B B B B No. 76 Example 4.23 98.7 157 B B A B No. 77 Example 3.21 98.4 159 B B B B No. 78 Example 3.36 98.1 150 B B C B No. 79 Example 6.18 97.9 146 C C C C No. 80 Compar- 3.77 96.6 129 D D B D ative Example No. 81 Compar- 3.94 96.9 136 D D B D ative Example No. 82 Compar- 3.65 96.4 128 E E C E ative Example No. 83 Compar- 4.87 94.9 119 D D D D ative Example No. 84 Compar- 4.25 94.8 125 D D E D ative Example No. 85 Compar- 3.77 99.3 180 A A B A ative Example

TABLE 10 Metal powder Average particle Cr(0)/ Si(0)/ O(0)/ Sample diameter Cr(0) Cr(60) Cr(60) Si(0) Si(60) Si(60) O(0) Si(0) No. — μm at % at % % at % at % % at % — No. 86 Example 4.32 2.4 2.1 114.3 42.3 15.4 274.7 7.8 0.18 No. 87 Example 4.31 3.2 2.4 133.3 39.8 16.3 244.2 8.2 0.21 No. 88 Example 7.32 2.8 2.3 121.7 36.8 13.1 280.9 9.2 0.25 No. 89 Compar- 4.12 4.5 2.1 214.3 18.4 9.8 187.8 14.5 0.79 ative Example No. 90 Example 6.19 1.2 0.8 15.0 44.5 19.5 228.2 6.8 0.15 No. 91 Example 4.45 0.9 1.0 90.0 48.2 22.1 218.1 9.4 0.20 No. 92 Example 7.29 1.0 0.9 111.1 45.3 18.7 242.2 8.5 0.19 No. 93 Compar- 4.18 0.7 1.1 63.6 21.5 17.2 125.0 12.6 0.59 ative Example No. 94 Example 3.86 5.6 4.5 124.4 38.5 18.2 211.5 7.8 0.20 No. 95 Example 3.92 7.2 6.5 110.8 39.7 19.4 204.6 6.8 0.17 No. 96 Example 4.02 6.8 6.9 98.6 40.2 15.9 252.8 5.9 0.15 No. 97 Compar- 3.48 9.5 5.4 175.9 25.6 16.9 151.5 13.1 0.51 ative Example No. 98 Example 4.05 9.1 7.3 124.7 36.7 18.3 200.5 8.1 0.22 No. 99 Example 9.85 9.3 7.5 124.0 37.1 16.4 226.2 7.9 0.21 No. 100 Example 8.42 8.7 8.9 97.8 35.4 15.9 222.6 7.5 0.21 No. 101 Compar- 4.02 12.5 7.1 176.1 28.1 18.5 151.9 13.6 0.48 ative Example Evaluation results of sintered body 0.2% Relative Vickers Tensile proof Elonga- Relative Sample density hardness strength stress tion density No. — % — — — — — No. 86 Example 99.7 — — — — — No. 87 Example 98.6 — — — — — No. 88 Example 98.7 — — — — — No. 89 Compar- 97.6 — — — — — ative Example No. 90 Example 98.7 — — — — — No. 91 Example 98.3 — — — — — No. 92 Example 98.1 — — — — — No. 93 Compar- 96.9 — — — — — ative Example No. 94 Example 99.5 — — — — — No. 95 Example 99.3 — — — — — No. 96 Example 99.4 — — — — — No. 97 Compar- 94.5 — — — — — ative Example No. 98 Example 99.5 — — — — — No. 99 Example 98.7 — — — — — No. 100 Example 98.6 — — — — — No. 101 Compar- 96.6 — — — — — ative Example

As apparent from Tables 6 to 10, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example (excluding the sintered bodies having undergone the HIP treatment). Further, it was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, elongation, and fatigue strength between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example (excluding the sintered bodies having undergone the HIP treatment).

On the other hand, by comparison of the values of the respective physical properties between the sintered bodies corresponding to Example and the sintered bodies having undergone the HIP treatment, it was confirmed that the values of the physical properties are all comparable to each other.

4. Production of Sintered Body (Hf—Nb Based) Sample Nos. 102 to 145

Sintered bodies were obtained in the same manner as the method for producing the sintered body of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Tables 11 to 14, respectively.

TABLE 11 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Hf) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 102 Example 16.25 12.56 0.71 0.02 0.09 0.05 2.09 0.05 0.25 remainder 1.80 0.14 0.20 8.24 No. 103 Example 17.14 12.54 0.57 0.02 0.07 0.05 2.45 0.09 0.32 remainder 1.40 0.12 0.21 5.45 No. 104 Example 17.78 13.25 0.53 0.03 0.07 0.08 2.06 0.08 0.41 remainder 0.88 0.15 0.28 5.56 No. 105 Example 16.25 14.68 0.82 0.01 0.06 0.03 2.89 0.08 0.25 remainder 2.00 0.09 0.11 7.50 No. 106 Example 17.52 13.87 0.74 0.03 0.09 0.10 2.63 0.11 0.34 remainder 0.90 0.19 1.26 7.31 No. 107 Example 16.82 12.03 0.53 0.07 0.11 0.04 2.76 0.11 0.23 remainder 2.75 0.15 0.28 2.17 No. 108 Example 17.52 13.25 0.68 0.06 0.07 0.12 2.21 0.78 0.41 remainder 0.58 0.19 0.28 3.45 No. 109 Example 16.34 12.84 0.75 0.03 0.00 0.07 2.36 0.11 0.29 remainder 0.00 0.07 0.09 2.80 No. 110 Compar- 17.25 13.35 0.82 0.03 0.08 0.00 2.23 0.09 0.32 remainder — 0.08 0.10 2.86 ative Example No. 111 Compar- 16.75 14.23 0.75 0.02 0.00 0.00 2.33 0.12 0.33 remainder — 0.00 0.00 0.00 ative Example No. 112 Compar- 16.34 12.54 0.87 0.02 0.71 0.05 2.56 0.11 0.36 remainder 14.20  0.76 0.87 36.19 ative Example No. 113 Compar- 16.44 13.12 0.65 0.03 0.04 0.68 2.41 0.06 0.42 remainder 0.06 0.72 1.11 21.18 ative Example No. 114 Compar- 17.63 13.21 0.14 0.01 0.06 0.07 2.77 0.11 0.27 remainder 0.86 0.13 0.93 10.83 ative Example No. 115 Compar- 17.54 13.33 1.91 0.05 0.07 0.05 2.68 0.34 0.48 remainder 1.40 0.12 0.06 2.22 ative Example

TABLE 12 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Hf) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 116 Example 18.96 13.54 0.82 0.041 0.09 0.05 3.55 0.35 0.41 remainder 1.80 0.14 0.17 3.41 No. 117 Example 18.25 14.86 0.54 0.021 0.06 0.09 3.12 0.87 0.39 remainder 0.67 0.15 0.28 7.14 No. 118 Example 19.74 11.32 0.34 0.067 0.09 0.09 3.88 0.45 0.55 remainder 1.00 0.18 0.53 2.69 No. 119 Compar- 18.67 11.36 0.78 0.053 0.00 0.07 3.47 0.22 0.29 remainder 0.00 0.07 0.09 1.32 ative Example No. 120 Compar- 19.54 14.35 0.89 0.022 0.11 0.00 3.75 0.09 0.31 remainder — 0.11 0.12 5.00 ative Example No. 121 Compar- 18.69 11.87 0.71 0.027 0.54 0.07 3.76 0.12 0.38 remainder 7.71 0.61 0.86 22.59 ative Example No. 122 Compar- 19.42 14.58 0.62 0.024 0.06 0.66 3.54 0.07 0.41 remainder 0.09 0.72 1.16 30.00 ative Example

TABLE 13 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Hf) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 123 Example 19.21 8.25 0.67 0.035 0.08 0.05 0.00 0.18 0.25 remainder 1.60 0.13 0.19 3.71 No. 124 Example 19.74 8.62 0.89 0.039 0.06 0.09 0.05 0.08 0.29 remainder 0.67 0.15 0.17 3.85 No. 125 Example 18.30 10.31 0.43 0.017 0.14 0.09 0.03 0.23 0.41 remainder 1.56 0.23 0.53 13.53 No. 126 Compar- 19.11 8.23 0.77 0.055 0.00 0.06 0.00 0.14 0.25 remainder 0.00 0.06 0.08 1.09 ative Example No. 127 Compar- 18.78 9.45 0.76 0.024 0.07 0.00 0.02 0.11 0.29 remainder — 0.07 0.09 2.92 ative Example No. 128 Compar- 18.42 8.36 0.38 0.011 0.54 0.08 0.03 0.25 0.28 remainder 6.75 0.62 1.63 56.36 ative Example No. 129 Compar- 19.21 8.45 0.45 0.018 0.06 0.58 0.04 0.16 0.32 remainder 0.10 0.64 1.42 35.56 ative Example

TABLE 14 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Hf) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 130 Example 3.92 0.07 0.71 1.425 0.10 0.05 5.06 0.00 0.18 remainder 2.00 0.15 0.21 0.11 W: 6.07 Co: 8.47 No. 131 Example 4.32 0.21 0.83 1.395 0.05 0.06 4.75 0.00 0.27 remainder 0.83 0.11 0.13 0.08 W: 6.56 Co: 8.14 No. 132 Example 4.12 0.13 0.76 1.425 0.15 0.05 4.87 0.00 0.27 remainder 3.00 0.20 0.26 0.14 W: 5.87 Co: 8.26 No. 133 Compar- 4.11 0.06 0.79 1.426 0.06 0.00 5.11 0.00 0.23 remainder — 0.06 1.08 0.04 W: 6.08 ative Co: 8.58 Example No. 134 Example 1.08 0.03 0.75 0.712 0.14 0.08 0.23 0.72 0.24 remainder 1.75 0.22 1.29 0.31 No. 135 Example 0.92 0.00 0.86 0.707 0.21 0.06 0.23 0.77 0.23 remainder 3.50 0.27 0.31 0.38 No. 136 Example 1.06 0.08 0.80 0.725 0.04 0.05 0.28 0.68 0.21 remainder 0.80 0.09 0.11 0.12 Al: 0.03 No. 137 Compar- 0.97 0.15 0.77 0.704 0.18 0.00 0.28 0.85 0.34 remainder — 0.18 0.23 0.26 Al: 0.06 ative Example No. 138 Example 12.85 0.08 0.72 0.910 0.09 0.05 0.00 0.11 0.29 remainder 1.80 0.14 0.19 0.15 No. 139 Example 13.42 0.11 0.65 0.840 0.11 0.06 0.00 0.08 0.24 remainder 1.83 0.17 0.26 0.20 No. 140 Example 12.55 0.07 0.75 0.960 0.06 0.08 0.00 0.11 0.31 remainder 0.75 0.14 0.19 0.15 No. 141 Compar- 12.97 0.11 0.76 0.750 0.06 0.00 0.00 0.09 0.32 remainder — 0.06 0.08 0.08 ative Example No. 142 Example 16.45 4.18 0.75 0.019 0.13 0.32 0.00 0.00 0.29 remainder 0.41 0.45 0.60 23.68 Cu: 3.89 No. 143 Example 16.17 3.87 0.39 0.045 0.07 0.28 0.00 0.00 0.24 remainder 0.25 0.35 0.90 7.78 Cu: 4.54 No. 144 Example 16.87 4.03 1.58 0.067 0.16 0.18 0.00 0.00 0.35 remainder 0.89 0.34 0.22 5.07 Cu: 4.75 No. 145 Compar- 17.22 3.56 0.64 0.025 0.09 0.00 0.00 0.00 0.33 remainder — 0.09 1.14 3.60 Cu: 4.33 ative Example

In Tables 11 to 14, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Tables 11 to 14 is omitted.

5. Evaluation of Metal Powder (Hf—Nb Based)

With respect to the particles of the respective sample Nos., the content of Cr on the surface of the particle (Cr(0)), the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)), the content of Si on the surface of the particle (Si(0)), the content of Si at a depth of 60 nm from the surface of the particle (Si(60)), and the content of O on the surface of the particle (O(0)) were determined.

The determined contents are shown in Tables 15 and 18.

As apparent from Tables 15 and 18, it is confirmed that in the particles of the metal powders corresponding to Example, the content of Cr on the surface (Cr(0)) falls within the range of 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)).

Further, it is also confirmed that the content of Cr on the surface of the particle 1 (Cr(0)) falls within the range of 0.2% by atom or more and 15% by atom or less.

6. Evaluation of Sintered Body (Hf—Nb Based) 6.1 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Tables 11 to 14, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Tables 15 to 18.

6.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Tables 11 to 14, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Tables 15 to 18.

6.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Tables 11 to 13, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the values of the physical properties of the sintered bodies of the respective sample Nos. shown in Table 11 were evaluated according to the above-mentioned evaluation criteria applied to the Tables 6 and 9, and the values of the physical properties of the sintered bodies of the respective sample Nos. shown in Tables 12 and 13 were evaluated according to the above-mentioned evaluation criteria applied to the Tables 7 and 8.

The above evaluation results are shown in Tables 15 to 17.

TABLE 15 Metal powder Evaluation results of sintered body Average 0.2% particle Cr(0)/ Si(0)/ O(0)/ Relative Vickers Tensile proof Elonga- Sample diameter Cr(0) Cr(60) Cr(60) Si(0) Si(60) Si(60) O(0) Si(0) density hardness strength stress tion No. — μm at % at % % at % at % % at % — % — — — — No. 102 Example 4.12  9.7 7.5 129.3 35.8 18.1 197.8  8.5 0.24 99.5 162 A A A No. 103 Example 4.25  6.9 8.7  79.3 40.8 17.2 237.2  9.7 0.24 99.3 173 A A A No. 104 Example 4.02 12.1 7.9 153.2 27.8  7.5 370.7  7.8 0.28 98.7 160 A A A No. 105 Example 3.88 — — — — — — — — 98.5 153 B A A No. 106 Example 4.56 — — — — — — — — 98.9 175 A A A No. 107 Example 3.98 — — — — — — — — 99.2 170 A A A No. 108 Example 3.77 — — — — — — — — 98.2 185 B B B No. 109 Compar- 3.86 21.2 10.1  209.9 21.8 15.4 141.6 10.3 0.47 96.4 185 D D B ative Example No. 110 Compar- 3.95 19.7 10.5  187.6 20.1 13.4 150.0 13.2 0.66 96.8 180 D D B ative Example No. 111 Compar- 4.05 18.7 9.4 198.9 24.6 17.8 138.2 11.4 0.46 96.2 192 E E C ative Example No. 112 Compar- 4.57 — — — — — — — — 94.7 202 D D D ative Example No. 113 Compar- 4.52 — — — — — — — — 94.6 211 D D E ative Example No. 114 Compar- 3.65 — — — — — — — — 94.6 195 E E D ative Example No. 115 Compar- 3.28 — — — — — — — — 93.4 214 F F E ative Example

TABLE 16 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Sample diameter density hardness strength stress tion No. — μm % — — — — No. 116 Example 5.86 99.1 167 A A A No. 117 Example 4.97 98.9 170 A A A No. 118 Example 4.25 98.6 184 B B B No. 119 Compar- 5.31 96.3 195 D D B ative Example No. 120 Compar- 5.83 96.6 189 D D B ative Example No. 121 Compar- 4.52 95.1 201 D D D ative Example No. 122 Compar- 4.12 94.9 205 E E F ative Example

TABLE 17 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Sample diameter density hardness strength stress tion No. — μm % — — — — No. 123 Example 4.08 99.3 164 A A A No. 124 Example 3.58 99.0 175 A A A No. 125 Example 6.41 98.5 182 A A B No. 126 Compar- 3.98 96.3 195 D D B ative Example No. 127 Compar- 3.58 96.7 192 D D B ative Example No. 128 Compar- 4.35 94.7 205 D D E ative Example No. 129 Compar- 4.56 95.2 201 D D E ative Example

TABLE 18 Metal powder Evaluation results of sintered body Average 0.2% particle Cr(0)/ Si(0)/ O(0)/ Relative Vickers Tensile proof Elonga- Sample diameter Cr(0) Cr(60) Cr(6) Si(0) Si(60) Si(60) O(0) Si(0) density hardness strength stress tion No. — μm at % at % % at % at % % at % — % — — — — No. 130 Example 4.25 2.3 2.1 109.5 40.5 16.8 241.1 7.9 0.20 99.5 — — — — No. 131 Example 5.34 3.1 2.5 124.0 38.7 16.4 236.0 8.3 0.21 99.0 — — — — No. 132 Example 4.28 2.9 2.4 120.8 36.9 13.4 275.4 9.2 0.25 98.5 — — — — No. 133 Compar- 3.97 4.3 2.2 195.5 18.2 8.7 209.2 13.6 0.75 97.5 — — — — ative Example No. 134 Example 6.25 1.1 0.8 137.5 43.2 19.2 225.0 6.7 0.16 98.9 — — — — No. 135 Example 6.87 1 1 100.0 44.6 20.4 218.6 9.2 0.21 98.8 — — — — No. 136 Example 14.36 1.2 0.9 133.3 43.8 17.3 253.2 8.4 0.19 98.4 — — — — No. 137 Compar- 4.35 0.8 1.2 66.7 22.1 16.5 133.9 12.5 0.57 96.8 — — — — ative Example No. 138 Example 4.12 5.8 4.6 126.1 38.4 18.5 207.6 7.5 0.20 99.4 — — — — No. 139 Example 5.92 7.4 6.3 117.5 39.3 20.1 195.5 6.5 0.17 99.4 — — — — No. 140 Example 7.02 6.9 7.2 95.8 39.7 16.2 245.1 5.7 0.14 99.2 — — — — No. 141 Compar- 4.56 10.1 5.7 177.2 26.1 20.1 129.9 13.3 0.51 94.8 — — — — ative Example No. 142 Example 4.12 9.5 7.4 128.4 36.5 18.3 199.5 8.5 0.23 99.5 — — — — No. 143 Example 10.03 9.1 7.6 119.7 36.1 16.8 214.9 9.8 0.27 98.8 — — — — No. 144 Example 8.57 8.8 8.5 103.5 33.5 15.8 212.0 9.1 0.27 98.7 — — — — No. 145 Compar- 3.96 12.9 6.5 198.5 27.4 19.2 142.7 13.8 0.50 96.7 — — — — ative Example

As apparent from Tables 15 to 18, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

7. Production of Sintered Body (Ti—Nb Based) Sample Nos. 146 to 155

Sintered bodies were obtained in the same manner as the method for producing the sintered body of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 19, respectively.

Sample No. 156

A metal powder having an average particle diameter of 4.62 μm, a Ti powder having an average particle diameter of 40 μm, and a Nb powder having an average particle diameter of 25 μm were mixed, whereby a mixed powder was prepared. In the preparation of the mixed powder, each of the mixing amounts of the metal powder, the Ti powder, and the Nb powder was adjusted so that the composition of the mixed powder was as shown in Table 19.

Then, a sintered body was obtained in the same manner as the method for producing the sintered body of sample No. 1 using this mixed powder.

TABLE 19 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Ti) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 146 Example 16.52 12.54 0.77 0.015 0.08 0.07 2.13 0.06 0.25 remainder 1.14 0.15 0.19 10.00 No. 147 Example 16.86 13.15 0.51 0.021 0.08 0.08 2.21 0.51 0.42 remainder 1.00 0.16 0.31 7.62 No. 148 Example 16.63 11.87 0.81 0.025 0.06 0.10 2.07 0.35 0.24 remainder 0.60 0.16 0.20 6.40 No. 149 Example 17.12 12.61 0.98 0.065 0.04 0.18 2.23 0.07 0.54 remainder 0.22 0.22 0.22 3.38 No. 150 Example 16.23 13.54 0.51 0.009 0.04 0.08 2.26 0.02 0.35 remainder 0.50 0.12 0.24 13.33 No. 151 Example 17.85 12.35 0.42 0.125 0.09 0.08 2.57 0.35 0.25 remainder 1.13 0.17 0.40 1.36 No. 152 Compar- 16.87 11.42 0.56 0.056 0.00 0.08 2.47 0.12 0.25 remainder 0.00 0.08 0.14 1.43 ative Example No. 153 Compar- 17.56 14.51 0.78 0.032 0.12 0.00 2.68 0.11 0.33 remainder — 0.12 0.15 3.75 ative Example No. 154 Compar- 16.78 11.24 0.87 0.012 0.54 0.06 2.55 0.15 0.32 remainder 9.00 0.60 0.69 50.00 ative Example No. 155 Compar- 17.65 14.15 0.68 0.053 0.08 0.89 2.63 0.06 0.25 remainder 0.09 0.97 1.43 18.30 ative Example No. 156 Compar- 16.88 14.10 0.87 0.056 0.45 0.20 2.25 0.08 0.26 remainder 2.25 0.65 0.75 11.61 Mixed ative powder Example

In Table 19, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Table 19 is omitted.

8. Evaluation of Metal Powder (Ti—Nb Based)

With respect to the particles of the respective sample Nos., the content of Cr on the surface of the particle (Cr(0)), the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)), the content of Si on the surface of the particle (Si(0)), the content of Si at a depth of 60 nm from the surface of the particle (Si(60)), and the content of O on the surface of the particle (O(0)) were determined.

As a result, in the particles of the metal powders corresponding to Example, the content of Cr on the surface (Cr(0)) fell within the range of 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)).

Further, the content of Cr on the surface of the particle (Cr(0)) fell within the range of 0.2% by atom or more and 15% by atom or less.

On the other hand, in the particles of the metal powders corresponding to Comparative Example, the content of Cr on the surface (Cr(0)) did not fall within the above-mentioned range.

9. Evaluation of Sintered Body (Ti—Nb Based) 9.1 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 19, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 20.

9.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 19, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 20.

9.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 19, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-mentioned evaluation criteria applied to the Tables 6 and 9.

The above evaluation results are shown in Table 20.

TABLE 20 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Sample diameter density hardness strength stress tion No. — μm % — — — — No. 146 Example 4.34 97.9 179 A A A No. 147 Example 4.79 99.3 178 A A A No. 148 Example 4.05 99.4 175 A A A No. 149 Example 3.89 98.7 180 B B A No. 150 Example 4.12 98.5 185 B B B No. 151 Example 4.26 98.2 189 B B C No. 152 Compar- 4.31 96.5 191 D D B ative Example No. 153 Compar- 4.48 96.6 189 D D B ative Example No. 154 Compar- 4.25 95.3 205 D D D ative Example No. 155 Compar- 4.36 94.7 215 E E F ative Example No. 156 Compar- 4.62 95.9 214 E E F ative Example

As apparent from Table 20, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

10. Production of Sintered Body (Nb—Ta Based) Sample Nos. 157 to 166

Sintered bodies were obtained in the same manner as the method for producing the sintered body of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 21, respectively.

TABLE 21 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Nb) (Ta) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 157 Example 16.21 12.15 0.63 0.035 0.07 0.12 2.21 0.06 0.38 remainder 0.58 0.19 0.30 5.43 No. 158 Example 16.74 11.36 0.87 0.042 0.05 0.10 2.26 0.05 0.45 remainder 0.50 0.15 0.17 3.57 No. 159 Example 16.30 10.25 0.45 0.018 0.12 0.09 2.68 0.08 0.58 remainder 1.33 0.21 0.47 11.67 No. 160 Example 16.35 13.68 1.03 0.067 0.05 0.08 2.77 0.06 0.22 remainder 0.63 0.13 0.13 1.94 No. 161 Example 16.45 14.18 0.86 0.009 0.03 0.04 2.45 0.00 0.45 remainder 0.75 0.07 0.08 7.78 No. 162 Example 16.25 12.35 0.47 0.123 0.15 0.09 2.12 0.08 0.48 remainder 1.67 0.24 0.51 1.95 No. 163 Compar- 17.11 12.29 0.74 0.064 0.00 0.05 2.18 0.15 0.29 remainder 0.00 0.05 0.07 0.78 ative Example No. 164 Compar- 16.78 12.48 0.79 0.023 0.08 0.00 2.06 0.12 0.33 remainder — 0.08 0.10 3.48 ative Example No. 165 Compar- 16.42 13.65 0.39 0.012 0.69 0.07 2.89 0.08 0.37 remainder 9.86 0.76 1.95 63.33 ative Example No. 166 Compar- 17.21 10.88 0.42 0.021 0.06 0.61 2.98 0.13 0.35 remainder 0.10 0.67 1.60 31.90 ative Example

In Table 21, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Table 21 is omitted.

11. Evaluation of Metal Powder (Nb—Ta Based)

With respect to the particles of the respective sample Nos., the content of Cr on the surface of the particle (Cr(0)), the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)), the content of Si on the surface of the particle (Si(0)), the content of Si at a depth of 60 nm from the surface of the particle (Si(60)), and the content of O on the surface of the particle (O(0)) were determined.

As a result, in the particles of the metal powders corresponding to Example, the content of Cr on the surface (Cr(0)) fell within the range of 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)).

Further, the content of Cr on the surface of the particle (Cr(0)) fell within the range of 0.2% by atom or more and 15% by atom or less.

On the other hand, in the particles of the metal powders corresponding to Comparative Example, the content of Cr on the surface (Cr(0)) did not fall within the above-mentioned range.

12. Evaluation of Sintered Body (Nb—Ta Based) 12.1 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 21, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 22.

12.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 21, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 22.

12.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 21, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-mentioned evaluation criteria applied to Tables 6 and 9.

The above evaluation results are shown in Table 22.

TABLE 22 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Sample diameter density hardness strength stress tion No. — μm % — — — — No. 157 Example 3.87 99.0 166 A A A No. 158 Example 4.12 99.1 167 A A B No. 159 Example 6.45 98.5 173 A A B No. 160 Example 5.82 98.3 178 B B B No. 161 Example 3.45 98.2 175 B B B No. 162 Example 3.25 97.4 181 B B C No. 163 Compar- 3.98 96.3 181 D D B ative Example No. 164 Compar- 3.74 96.0 187 D D B ative Example No. 165 Compar- 4.21 93.8 236 D D D ative Example No. 166 Compar- 3.87 94.2 225 D D E ative Example

As apparent from Table 22, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

13. Production of Sintered Body (Y—Nb Based) Sample Nos. 167 to 177

Sintered bodies were obtained in the same manner as the method for producing the sintered body of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 23, respectively.

TABLE 23 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Y) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 167 Example 16.55 12.58 0.85 0.025 0.08 0.09 2.13 0.07 0.26 remainder 0.89 0.17 0.20 6.80 No. 168 Example 17.32 12.87 0.68 0.023 0.05 0.08 2.21 0.11 0.33 remainder 0.63 0.13 0.19 5.65 No. 169 Example 16.35 12.32 0.74 0.029 0.09 0.05 2.04 0.08 0.41 remainder 1.80 0.14 0.19 4.83 No. 170 Example 16.31 14.52 0.53 0.011 0.03 0.08 2.68 0.07 0.26 remainder 0.38 0.11 0.21 10.00 No. 171 Example 17.12 13.88 0.57 0.024 0.09 0.10 2.51 0.12 0.34 remainder 0.90 0.19 0.33 7.92 No. 172 Example 16.66 11.58 1.02 0.057 0.11 0.04 2.74 0.12 0.22 remainder 2.75 0.15 0.15 2.63 No. 173 Example 16.21 13.21 0.32 0.044 0.08 0.21 2.15 0.79 0.41 remainder 0.67 0.20 0.63 4.55 No. 174 Compar- 16.55 12.74 0.84 0.026 0.00 0.06 2.24 0.13 0.32 remainder 0.00 0.06 0.17 2.31 ative Example No. 175 Compar- 17.25 12.79 0.74 0.023 0.07 0.00 2.21 0.06 0.27 remainder — 0.07 0.09 3.04 ative Example No. 176 Compar- 16.87 12.36 0.86 0.029 0.64 0.12 2.64 0.21 0.41 remainder 5.33 0.76 0.88 26.21 ative Example No. 177 Compar- 16.39 13.11 0.71 0.033 0.08 0.72 2.35 0.06 0.39 remainder 0.11 0.80 1.13 24.24 ative Example

In Table 23, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Table 23 is omitted.

14. Evaluation of Metal Powder (Y—Nb Based)

With respect to the particles of the respective sample Nos., the content of Cr on the surface of the particle (Cr(0)), the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)), the content of Si on the surface of the particle (Si(0)), the content of Si at a depth of 60 nm from the surface of the particle (Si(60)), and the content of O on the surface of the particle (O(0)) were determined.

As a result, in the particles of the metal powders corresponding to Example, the content of Cr on the surface (Cr(0)) fell within the range of 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)).

Further, the content of Cr on the surface of the particle (Cr(0)) fell within the range of 0.2% by atom or more and 15% by atom or less.

On the other hand, in the particles of the metal powders corresponding to Comparative Example, the content of Cr on the surface (Cr(0)) did not fall within the above-mentioned range.

15. Evaluation of Sintered Body (Y—Nb Based) 15.1 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 23, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 24.

15.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 23, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 24.

15.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 23, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-mentioned evaluation criteria applied to Tables 6 and 9.

The above evaluation results are shown in Table 24.

TABLE 24 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Sample diameter density hardness strength stress tion No. — μm % — — — — No. 167 Example 4.11 99.2 169 A A A No. 168 Example 3.89 99.1 170 A A A No. 169 Example 3.94 99.0 172 A A A No. 170 Example 4.23 98.7 177 B A A No. 171 Example 4.12 99.2 174 A A A No. 172 Example 3.87 98.5 180 B B B No. 173 Example 3.69 98.4 181 B B B No. 174 Compar- 3.77 96.1 192 D D B ative Example No. 175 Compar- 3.94 95.9 196 D D B ative Example No. 176 Compar- 4.78 94.8 201 D E E ative Example No. 177 Compar- 4.56 94.6 204 D E E ative Example

As apparent from Table 24, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

16. Production of Sintered Body (V—Nb Based) Sample Nos. 178 to 187

Sintered bodies were obtained in the same manner as the method for producing the sintered body of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 25, respectively.

TABLE 25 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (V) (Nb) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 178 Example 16.56 12.65 0.79 0.025 0.08 0.15 2.35 0.06 0.26 remainder 0.53 0.23 0.29 9.20 No. 179 Example 16.42 12.36 0.71 0.016 0.05 0.10 2.28 0.09 0.31 remainder 0.50 0.15 0.21 9.38 No. 180 Example 17.23 12.15 0.89 0.022 0.15 0.12 2.23 0.07 0.68 remainder 1.25 0.27 0.30 12.27 No. 181 Example 17.89 11.75 0.97 0.047 0.09 0.09 2.59 0.05 0.18 remainder 1.00 0.18 0.19 3.83 No. 182 Example 18.23 13.21 0.88 0.011 0.05 0.10 2.87 0.07 0.31 remainder 0.50 0.15 0.17 13.64 No. 183 Example 18.25 10.25 0.44 0.187 0.12 0.12 2.47 0.07 0.47 remainder 1.00 0.24 0.55 1.28 No. 184 Compar- 16.54 12.74 0.58 0.056 0.00 0.06 2.68 0.12 0.28 remainder 0.00 0.06 0.10 1.07 ative Example No. 185 Compar- 16.39 12.47 0.75 0.032 0.09 0.00 2.13 0.11 0.32 remainder — 0.09 0.12 2.81 ative Example No. 186 Compar- 17.87 12.48 0.36 0.014 0.68 0.09 2.54 0.18 0.44 remainder 7.56 0.77 2.14 55.00 ative Example No. 187 Compar- 17.65 12.77 0.47 0.023 0.07 0.63 2.77 0.16 0.39 remainder 0.11 0.70 1.49 30.43 ative Example

In Table 25, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Table 25 is omitted.

17. Evaluation of Metal Powder (V—Nb Based)

With respect to the particles of the respective sample Nos., the content of Cr on the surface of the particle (Cr(0)), the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)), the content of Si on the surface of the particle (Si(0)), the content of Si at a depth of 60 nm from the surface of the particle (Si(60)), and the content of O on the surface of the particle (O(0)) were determined.

As a result, in the particles of the metal powders corresponding to Example, the content of Cr on the surface (Cr(0)) fell within the range of 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)).

Further, the content of Cr on the surface of the particle (Cr(0)) fell within the range of 0.2% by atom or more and 15% by atom or less.

On the other hand, in the particles of the metal powders corresponding to Comparative Example, the content of Cr on the surface (Cr(0)) did not fall within the above-mentioned range.

18. Evaluation of Sintered Body (V—Nb Based) 18.1 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 25, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 26.

18.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 25, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 26.

18.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 25, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-mentioned evaluation criteria applied to Tables 6 and 9.

The above evaluation results are shown in Table 26.

TABLE 26 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Sample diameter density hardness strength stress tion No. — μm % — — — — No. 178 Example 4.12 98.9 172 A A B No. 179 Example 4.25 99.0 167 A A A No. 180 Example 6.89 98.5 175 A A B No. 181 Example 5.74 98.3 181 B B B No. 182 Example 3.25 98.7 161 B B A No. 183 Example 4.11 97.4 194 B B C No. 184 Compar- 3.98 96.2 202 D D C ative Example No. 185 Compar- 3.74 96.0 211 D D C ative Example No. 186 Compar- 4.52 94.5 215 D D D ative Example No. 187 Compar- 3.45 94.3 223 D D E ative Example

As apparent from Table 26, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

19. Production of Sintered Body (Ti—Zr Based) Sample Nos. 188 to 197

Sintered bodies were obtained in the same manner as the method for producing the sintered body of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 27, respectively.

TABLE 27 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Ti) (Zr) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 188 Example 16.85 12.74 0.86 0.023 0.06 0.12 2.54 0.07 0.31 remainder 0.50 0.18 0.21 7.83 No. 189 Example 17.24 12.14 0.74 0.039 0.05 0.10 2.36 0.04 0.49 remainder 0.50 0.15 0.20 3.85 No. 190 Example 16.21 12.46 0.62 0.019 0.12 0.09 2.78 0.07 0.54 remainder 1.33 0.21 0.34 11.05 No. 191 Example 16.57 12.98 0.97 0.059 0.08 0.06 2.23 0.05 0.21 remainder 1.33 0.14 0.14 2.37 No. 192 Example 17.85 12.41 0.88 0.009 0.05 0.10 2.74 0.07 0.35 remainder 0.50 0.15 0.17 16.67 No. 193 Example 17.65 13.21 0.44 0.175 0.09 0.09 2.68 0.07 0.44 remainder 1.00 0.18 0.41 1.03 No. 194 Compar- 17.44 12.47 0.72 0.055 0.00 0.06 2.75 0.18 0.26 remainder 0.00 0.06 0.08 1.09 ative Example No. 195 Compar- 16.54 12.87 0.78 0.032 0.09 0.00 2.69 0.08 0.35 remainder — 0.09 0.12 2.81 ative Example No. 196 Compar- 16.32 13.58 0.38 0.021 0.64 0.08 2.41 0.09 0.28 remainder 8.00 0.72 1.89 34.29 ative Example No. 197 Compar- 16.25 13.75 0.43 0.018 0.07 0.59 2.21 0.06 0.22 remainder 0.12 0.66 1.53 36.67 ative Example

In Table 27, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Table 27 is omitted.

20. Evaluation of Metal Powder (Ti—Zr Based)

With respect to the particles of the respective sample Nos., the content of Cr on the surface of the particle (Cr(0)), the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)), the content of Si on the surface of the particle (Si(0)), the content of Si at a depth of 60 nm from the surface of the particle (Si(60)), and the content of O on the surface of the particle (O(0)) were determined.

As a result, in the particles of the metal powders corresponding to Example, the content of Cr on the surface (Cr(0)) fell within the range of 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)).

Further, the content of Cr on the surface of the particle (Cr(0)) fell within the range of 0.2% by atom or more and 15% by atom or less.

On the other hand, in the particles of the metal powders corresponding to Comparative Example, the content of Cr on the surface (Cr(0)) did not fall within the above-mentioned range.

21. Evaluation of Sintered Body (Ti—Zr Based) 21.1 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 27, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 28.

21.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 27, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 28.

21.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 27, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-mentioned evaluation criteria applied to Tables 6 and 9.

The above evaluation results are shown in Table 28.

TABLE 28 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Sample diameter density hardness strength stress tion No. — μm % — — — — No. 188 Example 4.12 98.8 172 A A B No. 189 Example 4.25 99.0 167 A A A No. 190 Example 5.87 98.6 184 A A B No. 191 Example 5.12 98.5 191 B B B No. 192 Example 3.89 98.2 195 B B B No. 193 Example 4.47 97.4 199 B B C No. 194 Compar- 4.11 96.3 205 D D C ative Example No. 195 Compar- 3.78 96.7 211 D D C ative Example No. 196 Compar- 4.52 94.7 235 D D E ative Example No. 197 Compar- 3.88 95.2 221 D D E ative Example

As apparent from Table 28, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

22. Production of Sintered Body (Zr—Ta Based) Sample Nos. 198 to 212

Sintered bodies were obtained in the same manner as the method for producing the sintered body of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Tables 29 and 30, respectively.

TABLE 29 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Zr) (Ta) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 198 Example 16.61 12.45 0.68 0.023 0.06 0.09 2.55 0.11 0.38 remainder 0.67 0.15 0.22 6.52 No. 199 Example 16.94 12.21 0.72 0.039 0.05 0.10 2.47 0.06 0.24 remainder 0.50 0.15 0.21 3.85 No. 200 Example 17.43 12.89 0.85 0.019 0.12 0.09 2.05 0.54 0.49 remainder 1.33 0.21 0.25 11.05 No. 201 Example 17.21 13.42 0.97 0.058 0.08 0.06 2.78 0.07 0.31 remainder 1.33 0.14 0.14 2.41 No. 202 Example 16.31 12.87 0.88 0.011 0.05 0.10 2.74 0.12 0.55 remainder 0.50 0.15 0.17 13.64 No. 203 Example 16.54 12.25 0.44 0.146 0.09 0.09 2.32 0.07 0.68 remainder 1.00 0.18 0.41 1.23 No. 204 Compar- 17.24 12.14 0.77 0.018 0.00 0.06 2.56 0.08 0.27 remainder 0.00 0.06 0.08 3.33 ative Example No. 205 Compar- 16.87 12.56 0.82 0.026 0.09 0.00 2.24 0.09 0.32 remainder — 0.09 0.11 3.46 ative Example No. 206 Compar- 16.54 12.32 0.35 0.025 0.78 0.05 2.89 0.11 0.35 remainder 15.60 0.83 2.37 33.20 ative Example No. 207 Compar- 16.35 12.47 0.45 0.022 0.04 0.58 2.77 0.16 0.33 remainder 0.07 0.62 1.38 28.18 ative Example

TABLE 30 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Zr) (Ta) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 208 Example 7.04 0.35 1.78 0.240 0.12 0.18 0.00 0.72 0.49 remainder 0.67 0.30 0.17 1.25 No. 209 Example 19.08 40.31 0.44 0.540 0.04 0.08 0.00 0.79 0.34 remainder 0.50 0.12 0.27 0.22 No. 210 Example 20.69 19.77 0.54 0.420 0.06 0.15 0.00 0.84 0.36 remainder 0.40 0.21 0.39 0.50 No. 211 Compar- 19.18 40.32 0.54 0.440 0.00 0.00 0.00 0.72 0.28 remainder — 0.00 0.00 0.00 ative Example No. 212 Compar- 19.31 39.58 0.75 0.480 0.07 0.00 0.00 0.86 0.43 remainder — 0.07 0.09 0.15 ative Example

In Tables 29 and 30, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Tables 29 and 30 is omitted.

23. Evaluation of Metal Powder (Zr—Ta Based)

With respect to the particles of the respective sample Nos., the content of Cr on the surface of the particle (Cr(0)), the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)), the content of Si on the surface of the particle (Si(0)), the content of Si at a depth of 60 nm from the surface of the particle (Si(60)), and the content of O on the surface of the particle (O(0)) were determined.

As a result, in the particles of the metal powders corresponding to Example, the content of Cr on the surface (Cr(0)) fell within the range of 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)).

Further, the content of Cr on the surface of the particle (Cr(0)) fell within the range of 0.2% by atom or more and 15% by atom or less.

On the other hand, in the particles of the metal powders corresponding to Comparative Example, the content of Cr on the surface (Cr(0)) did not fall within the above-mentioned range.

24. Evaluation of Sintered Body (Zr—Ta Based) 24.1 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Tables 29 and 30, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Tables 31 and 32.

24.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 29, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 31.

24.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 29, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-mentioned evaluation criteria applied to Tables 6 and 9.

The above evaluation results are shown in Table 31.

TABLE 31 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Sample diameter density hardness strength stress tion No. — μm % — — — — No. 198 Example 4.12 99.2 172 A A A No. 199 Example 4.32 99.3 167 A A A No. 200 Example 5.74 98.7 181 A A B No. 201 Example 5.21 98.5 185 B B B No. 202 Example 4.32 98.2 189 B B B No. 203 Example 4.23 97.5 197 B B C No. 204 Compar- 3.88 96.2 199 D D C ative Example No. 205 Compar- 4.22 96.2 199 D D C ative Example No. 206 Compar- 4.11 94.8 211 D D E ative Example No. 207 Compar- 3.89 95.1 205 D D E ative Example

TABLE 32 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Sample diameter density hardness strength stress tion No. — μm % — — — — No. 208 Example 14.46 98.7 — — — — No. 209 Example 7.45 98.6 — — — — No. 210 Example 6.58 99.0 — — — — No. 211 Compar- 7.98 96.1 — — — — ative Example No. 212 Compar- 8.02 95.4 — — — — ative Example

As apparent from Tables 31 and 32, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

25. Production of Sintered Body (Zr—V Based) Sample Nos. 213 to 227

Sintered bodies were obtained in the same manner as the method for producing the sintered body of sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Tables 33 and 34, respectively.

TABLE 33 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Zr) (V) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 213 Example 16.58 12.47 0.75 0.022 0.09 0.06 2.36 0.08 0.31 remainder 1.50 0.15 0.20 6.82 No. 214 Example 16.32 12.24 0.89 0.015 0.05 0.08 2.64 0.06 0.25 remainder 0.63 0.13 0.15 8.67 No. 215 Example 16.87 12.55 0.98 0.025 0.09 0.09 2.88 0.07 0.39 remainder 1.00 0.18 0.18 7.20 No. 216 Example 17.28 12.36 0.54 0.069 0.12 0.06 2.12 0.05 0.23 remainder 2.00 0.18 0.33 2.61 No. 217 Example 17.59 12.98 0.88 0.012 0.08 0.08 2.58 0.02 0.45 remainder 1.00 0.16 0.18 13.33 No. 218 Example 17.25 12.78 0.44 0.118 0.09 0.09 2.68 0.07 0.61 remainder 1.00 0.18 0.41 1.53 No. 219 Compar- 16.34 12.63 0.77 0.054 0.00 0.06 2.84 0.08 0.36 remainder 0.00 0.06 0.08 1.11 ative Example No. 220 Compar- 16.78 12.24 0.78 0.032 0.09 0.00 2.64 0.11 0.27 remainder — 0.09 0.12 2.81 ative Example No. 221 Compar- 16.24 12.36 0.38 0.021 0.61 0.08 2.31 0.09 0.18 remainder 7.63 0.69 1.82 32.86 ative Example No. 222 Compar- 17.12 12.89 0.45 0.025 0.08 0.59 2.15 0.05 0.24 remainder 0.14 0.62 1.49 26.80 ative Example

TABLE 34 Metal powder for powder metallurgy Alloy composition (E1 + (E1 + E1 E2 E1/ E1 + E2)/ E2)/ Re- Sample Cr Ni Si C (Zr) (V) Mo Mn O Fe E2 E2 Si C marks No. — mass % — mass % — — — No. 223 Example 7.12 0.38 1.74 0.260 0.11 0.17 0.00 0.92 0.45 remainder 0.65 0.28 0.16 1.08 No. 224 Example 19.22 40.25 0.43 0.480 0.05 0.03 0.00 0.75 0.36 remainder 1.67 0.08 0.19 0.17 No. 225 Example 20.64 19.68 0.89 0.360 0.09 0.05 0.00 0.84 0.36 remainder 1.80 0.14 0.16 0.39 No. 226 Compar- 19.22 40.39 0.43 0.480 0.00 0.00 0.00 0.89 0.36 remainder — 0.00 0.00 0.00 ative Example No. 227 Compar- 19.28 39.66 0.73 0.490 0.08 0.00 0.00 0.99 0.45 remainder — 0.08 0.11 0.16 ative Example

In Tables 33 and 34, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated by “Example”, and those not corresponding to the invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but the description thereof in Tables 33 and 34 is omitted.

26. Evaluation of Metal Powder (Zr—V Based)

With respect to the particles of the respective sample Nos., the content of Cr on the surface of the particle (Cr(0)), the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)), the content of Si on the surface of the particle (Si(0)), the content of Si at a depth of 60 nm from the surface of the particle (Si(60)), and the content of O on the surface of the particle (O(0)) were determined.

As a result, in the particles of the metal powders corresponding to Example, the content of Cr on the surface (Cr(0)) fell within the range of 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle (Cr(60)).

Further, the content of Cr on the surface of the particle (Cr(0)) fell within the range of 0.2% by atom or more and 15% by atom or less.

On the other hand, in the particles of the metal powders corresponding to Comparative Example, the content of Cr on the surface (Cr(0)) did not fall within the above-mentioned range.

27. Evaluation of Sintered Body (Zr—V Based) 27.1 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Tables 33 and 34, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Tables 35 and 36.

27.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 33, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 35.

27.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 33, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-mentioned evaluation criteria applied to Tables 6 and 9.

The above evaluation results are shown in Table 35.

TABLE 35 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Sample diameter density hardness strength stress tion No. — μm % — — — — No. 213 Example 4.15 99.3 172 A A A No. 214 Example 4.26 98.9 167 A A B No. 215 Example 5.74 99.0 180 A A B No. 216 Example 5.12 99.1 178 B B B No. 217 Example 3.86 98.3 197 B B B No. 218 Example 3.65 97.5 202 B B C No. 219 Compar- 4.05 96.2 209 D D C ative Example No. 220 Compar- 4.13 96.5 208 D D C ative Example No. 221 Compar- 4.05 94.7 225 D D E ative Example No. 222 Compar- 3.88 95.2 212 D D E ative Example

TABLE 36 Metal powder Evaluation results of sintered body Average 0.2% particle Relative Vickers Tensile proof Elonga- Sample diameter density hardness strength stress tion No. — μm % — — — — No. 223 Example 12.68 98.6 — — — — No. 224 Example 7.27 98.5 — — — — No. 225 Example 6.39 99.0 — — — — No. 226 Compar- 7.87 96.2 — — — — ative Example No. 227 Compar- 7.99 95.5 — — — — ative Example

As apparent from Tables 35 and 36, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

28. Evaluation of Specularity of Sintered Body 28.1 Evaluation of Porosity Near Surface and Inside

First, each of the sintered bodies of the respective sample Nos. shown in Table 37 was cut and the cross section was polished.

Then, a porosity A1 near the surface of the sintered body and a porosity A2 inside the sintered body were calculated and also A2−A1 was calculated.

The above calculation results are shown in Table 37.

28.2 Evaluation of Specular Gloss

First, each of the sintered bodies of the respective sample Nos. shown in Table 37 was subjected to a barrel polishing treatment.

Then, the specular gloss of the sintered body was measured in accordance with the method for measuring the specular gloss specified in JIS Z 8741 (1997). The incident angle of light with respect to the surface of the sintered body was set to 60°, and as a reference plane for calculating the specular gloss, a glass having a specular gloss of 90 and a refractive index of 1.500 was used. Then, the measured specular gloss was evaluated according to the following evaluation criteria.

Evaluation Criteria for Specular Gloss

A: The specularity of the surface is very high (the specular gloss is 200 or more).

B: The specularity of the surface is high (the specular gloss is 150 or more and less than 200).

C: The specularity of the surface is slightly high (the specular gloss is 100 or more and less than 150).

D: The specularity of the surface is slightly low (the specular gloss is 60 or more and less than 100).

E: The specularity of the surface is low (the specular gloss is 30 or more and less than 60).

F: The specularity of the surface is very low (the specular gloss is less than 30).

The above evaluation results are shown in Table 37.

TABLE 37 Alloy Evaluation results Sample Example/ composition A2-A1 Specular No. Comparative Example E1 E2 [%] gloss 2 Example Zr Nb 1.0 A 23 Comparative Example 0.2 E 102 Example Hf Nb 0.9 A 111 Comparative Example 0.2 E 148 Example Ti Nb 1.2 A 152 Comparative Example 0.1 E 158 Example Nb Ta 0.6 C 163 Comparative Example 0.1 E 167 Example Y Nb 1.2 A 174 Comparative Example 0.2 E 179 Example V Nb 0.6 C 184 Comparative Example 0.1 E 189 Example Ti Zr 0.7 C 194 Comparative Example 0.1 E 199 Example Zr Ta 0.6 B 204 Comparative Example 0.2 E 213 Example Zr V 0.5 B 219 Comparative Example 0.2 E

As apparent from Table 37, it was confirmed that the sintered bodies corresponding to Example each have a higher specular gloss than the sintered bodies corresponding to Comparative Example. This is considered to be because the porosity near the surface of the sintered body is low, and therefore, light scattering is suppressed, however, the ratio of regular reflection is increased. 

What is claimed is:
 1. A metal powder for powder metallurgy, comprising particles, which contain Fe as a principal component, Cr in a proportion of 0.2% by mass or more and 35% by mass or less, Si in a proportion of 0.2% by mass or more and 3% by mass or less, and C in a proportion of 0.005% by mass or more and 2% by mass or less, and in which when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a higher group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a higher period number in the periodic table than that of the first element is defined as a second element, the first element is contained in a proportion of 0.01% by mass or more and 0.5% by mass or less, and the second element is contained in a proportion of 0.01% by mass or more and 0.5% by mass or less, wherein the content of Cr on the surface of each particle is 0.2% by atom or more and 15% by atom or less and is 70% or more and 170% or less the content of Cr at a depth of 60 nm from the surface of the particle.
 2. The metal powder for powder metallurgy according to claim 1, wherein the content of Si on the surface of each particle is 155% or more and 800% or less the content of Si at a depth of 60 nm from the surface of the particle.
 3. The metal powder for powder metallurgy according to claim 1, wherein the ratio of the content of O to the content of Si on the surface of each particle is 0.05 or more and 0.4 or less.
 4. The metal powder for powder metallurgy according to claim 1, wherein the content of Cr on the surface of each particle is lower than the content of Cr in the whole particle.
 5. The metal powder for powder metallurgy according to claim 1, wherein the ratio (X1/X2) of a value (X1) obtained by dividing the content (E1) of the first element by the mass number of the first element to a value (X2) obtained by dividing the content (E2) of the second element by the mass number of the second element is 0.3 or more and 3 or less.
 6. The metal powder for powder metallurgy according to claim 1, wherein the sum of the content of the first element and the content of the second element is 0.05% by mass or more and 0.8% by mass or less.
 7. The metal powder for powder metallurgy according to claim 1, wherein the metal powder has an average particle diameter of 0.5 μm or more and 30 μm or less.
 8. A compound, comprising the metal powder for powder metallurgy according to claim 1 and a binder which binds the particles of the metal powder for powder metallurgy to one another.
 9. A compound, comprising the metal powder for powder metallurgy according to claim 2 and a binder which binds the particles of the metal powder for powder metallurgy to one another.
 10. A compound, comprising the metal powder for powder metallurgy according to claim 3 and a binder which binds the particles of the metal powder for powder metallurgy to one another.
 11. A compound, comprising the metal powder for powder metallurgy according to claim 4 and a binder which binds the particles of the metal powder for powder metallurgy to one another.
 12. A granulated powder, wherein the granulated powder is obtained by granulating the metal powder for powder metallurgy according to claim
 1. 13. A granulated powder, wherein the granulated powder is obtained by granulating the metal powder for powder metallurgy according to claim
 2. 14. A granulated powder, wherein the granulated powder is obtained by granulating the metal powder for powder metallurgy according to claim
 3. 15. A granulated powder, wherein the granulated powder is obtained by granulating the metal powder for powder metallurgy according to claim
 4. 16. A sintered body, wherein the sintered body is produced by sintering the metal powder for powder metallurgy according to claim
 1. 17. A sintered body, wherein the sintered body is produced by sintering the metal powder for powder metallurgy according to claim
 2. 18. A sintered body, wherein the sintered body is produced by sintering the metal powder for powder metallurgy according to claim
 3. 19. A sintered body, wherein the sintered body is produced by sintering the metal powder for powder metallurgy according to claim
 4. 